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Protistologist to the Medical Research Council, London 
Foreign Member of the R. Accademia dei Lincei, Rome 
Sometime Fellow of Trinity College, Cambridge 











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The Epistle to the Reader : : : : : : 3 ; i 
The Life of Antony van Leeuwenhoek . 5 ‘ : eS) 
Chapter 1.—The First Observations on “ Little Animals ”’ 
(Protozoa and Bacteria) in Waters . : : ; . 109 
Chapter 2.—EHpilogue to Letter 18. Further Observations 
on the Free-living Protozoa and Bacteria . : . WOK 
Chapter 3.—The First Observations on Entozoic Protozoa 
and Bacteria ; ; : : é : : ‘ aly! 

Chapter 4.—The Later Observations on Free-living Protozoa 256 

Elucidations and Annotations 

(i) Leeuwenhoek’s name : : : : ; 3° 300 

(ii) Leeuwenhoek’s language ’ ; , : : 305 

(iii) Leeuwenhoek’s microscopes and microscopical mations 313 

(iv) Leeuwenhoek’s dwelling . , , eas 

(v) Leeuwenhoek’s draughtsmen . : ; : ‘ . 342 

(vi) The portraits of Leeuwenhoek : : ‘ . 3846 

(vii) Leeuwenhoek’s “ first 27 unpublished eee: ig : . 306 

(viii) Leeuwenhoek’s seals : : ; , ; 359 
Envoy : Leeuwenhoek’s Place in Protozoology and Bacteriology . 362 
Short List of Leeuwenhoek’s Writings . : : : : . 888 
Other References and Sources . ; ‘ : : : ‘ . 398 
Acknowledgements. : ' : ‘ ; : é : . 423 
Index , ‘ A ; ; ' : ; : ; : . 426 



The Gregorian correction of the Julian Calendar was not made simul- 
taneously in England and the Netherlands, and during Leeuwenhoek’s 
lifetime two different systems of dating—known as ° Old Style ” and “ New 
Style ’’—were current in these countries. 

“New Style” dating was adopted in the Provinces of Holland (wherein 
Delft is situated) and Brabant on 5 December 1582, which was called the 
15th of the month—thus advancing the Calendar by 10 days: though other 
Provinces of the Netherlands (Gelderland, Utrecht, Overyssel, Groningen, 
Friesland) did not recognize the new system until 1700. But in England 
the change was made even later, for it was not until 1752 that the Old 
Style ” was abolished by Act of Parliament. The discrepancy between the 
Julian and the Gregorian systems having become 11 days in the year 1700, 
the English Calendar was corrected by calling the 3rd of September (1752) 
the 14th. At the same time, the old Anglican method of commencing the 
year on March 25 (instead of January 1) was ended. Good Friday was 
New Year's Day in Delft before 1575, but not afterwards. 

All Leeuwenhoek’s own dates are therefore “New Style’’, and agree 
with modern reckoning. English dates of his period are, however, usually 
“Old Style’, and consequently to be understood as 10 days (from 1632 to 
1700) or 11 days (from 1700 to 1723) later in actual time. In the present 
work all dates of importance are given, as far as possible, in present-day 
form (N.S.) unless old-style dating (O.S.) is indicated. 



I.—Antony van Leeuwenhoek : from the mezzotint portrait by 

J. Verkolje (1686). , ; Frontispiece 
II.—_Leeuwenhoek’s birthplace . : : ; facing page 20 
IIJ.—Registration of Leeuwenhoek’s baptism . : : ota 
1V.—Oude Delft : . : ; . 25 
V.—Leeuwenhoek’s bill to P. Heeeieecer (1659) é ' . 80 
VI.—The Town Hall of Delft . j : : F 4 3S) oe 
VII.—Vermeer’s View of Delft . : 2 : : ; . | do 
VIII.—Portrait of Henry Oldenburg, Sec. R. S. . : : > oS 
IX.—Portrait of Dr Reinier de Graaf ‘ 40 
X.—Last lines of Leeuwenhoek’s Letter 2 (MS. 15 mae 1673) 49, 
XI.—Portrait of Leeuwenhoek: from Verkolje’s oil-painting . 49 
XII.—Miniature portrait of Leeuwenhoek by J. Goeree (1707) . 76 
XIII.—Last lines of Maria’s letter to the Royal Society : , 99 
XIV.—The Old Church at Delft . ; : : 5 a Oe 
X V.—Leeuwenhoek’s tomb in the Old Oia ‘ : : ec 
XV1I.—Portrait of H. Poot by T. van der Wilt . J 5 HO? 
XVII.—Facsimile of a passage from MS. of Letter 6. : 110 
XVIII.—First page of Oldenburg’s printed translation of Letter 18. 113 
XIX.—Facsimile of first page of MS. of Letter 18 ; : eG 
XX.—A House in Delft, after J. Vermeer . : : . 125 
XXI.—The Shore at Scheveningen, after J. v. Ruisdael . : s) £29 
XXII.—Illustration to Leeuwenhoek’s Letter 32 . , ; PtSi 
X XIIJI.—Leeuwenhoek’s pictures of Protozoa in Frogs . ; 233 
XXIV.—Leeuwenhoek’s pictures of Bacteria in the Human Macen 239 
XXV.—A page of the MS. of Letter 39 . : : 240 
XXVI.—Leeuwenhoek’s figures illustrating his account ee rane 
(Letter 122)  . 259 
XXVII.—The figures of Dances ind Aes (Lewes 125 é 144) 263 
XXVIII.—The Animalcules on Duckweed . ; F 277 
XXIX.— Last page of Letter about Duckweed (MS. 25 Thee 1702) . 285 
XXX.—The figures of Anthophysa vegetans (MS. 5 Feb. 1703) . 289 
XX XI.—Leeuwenhoek’s “ microscope’”’ . : F ; J . S28 

XX XIT.—Leeuwenhoek’s seals. : : E : . . 7 SoG 

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Introducing Mynher ANTONY van LEEUWENHOEK 
of Delft in Holland, Fellow of the Royal Society of London 
in England. 

Dear READER: I know full well that you and everyone else 
must have met Mr van Leeuwenhoek many a time before ; but 
please let me reintroduce him to you, for he is a man worth 
knowing more intimately. Though he was born exactly 300 
years ago he ws still very much alive, and would be glad to make 
your better acquaintance—provided only that you are “a true 
lover of learning” (as of course you are). But as his fleshly 
body ceased to work and dissolved in dust about a century 
before your grandfather came into the world, and as he himself 
knows no language but very old-fashioned Dutch, I think 
you will agree that an introducer and interpreter may not be 
superfluous and might even be helpful? So please let me tell 
you how I first met Mr Leeuwenhoek, and why I now presume 
to take these onerous offices wpon myself without any obvious 
call or qualification. Let me tell you why I, an almost un- 
known living Englishman, wish to make you more nearly 
familiar with a famous old Hollander who wrought and died 
long before we were born. 

When I was a very young man I began to study, for my 
own amusement, the microscopic creatures in organic infusions ; 
and in the cowrse of some desultory reading I then, to my 
surprise, discovered—a thing I ought, naturally, to have known— 
that these “ little animals” had originally been observed more 
than two centuries earlier by somebody called, more or less, 
Leeuwenhoek. (J say“ more or less” because I found his name 
spelled in a great variety of ways: and being then only some 
20 years of age, and having no knowledge of Dutch, I could not 
tell which way was right.) On looking into the matter, I found 
of course that this man with the strange patronymic was really 
a well-known figure in the History of Biology—notwithstanding 


my teachers had never told me of him (possibly, I now think, 
because they were wnable to utter his name). I found that he 
was honourably mentioned as a pioneer in many different fields 
of scientific research—his discovery of the Protozoa in infusions 
being only one of his many noteworthy achievements. An odd 
circumstance, which (I remember) struck me forcibly at the time, 
was that this old Hollander—for some reason unexplained— 
apparently made a practice of publishing his observations in 
English in our Philosophical Transactions, and was himself 
actually a Fellow of our own Royal Society of London. This 
then seemed to me very queer and inexplicable: yet had it not 
so happened, the present book would never have been written. 

After this my first meeting with Leeuwenhoek, 2 chanced 
that my studies led me away from the protozoa in infusions to 
those living inside frogs. I spent two or three painful years in 
their pursuit ; and in reading up the writings on the subject, I 
found again, to my astonishment, that the earliest observations 
on these organisms too had been made by the same person— 
Leeuwenhoek once more. This revived my interest in hin, and 
caused me to look into his publications anew. But I made little 
progress in my inquiries, because his original records were at that 
time inaccessible; and the second-hand sources of information 
then at my disposal were mostly worthless and contradictory— 
different authors supplying different references and statements, 
most of which turned out to be so incorrect that they led me 
nowhere. When I tried to find out something about the man 
himself, I met with no better success. Most writers agreed m 
calling him “well-known” or even “ celebrated”, and many 
called him “microscopist”’ or “naturalist” (all excellent epithets, 
as I now know). But some people said that he was “ a maker 
of lenses” and even “ the inventor of the microscope” (which 
even then I knew to be wrong), while others said he was a 
“physician”: and had I then looked further, I should have 
found that still others called him “ surgeon” and even“ Doctor” 
and “ Professor.” Yet all writers seemed to be wn agreement on 
one point, expressed or implied: and that was that they knew 
next to nothing about Leeuwenhoek himself, despite his alleged 
celebrity. No two writers gave the same account of him—even 
when copying one another. 

My own next researches (forgive me, dear Reader, for ob- 
truding myself in this fashion : it is unfortunately necessary for 
the present narrative) were largely concerned with the Bacterta— 


including those in the human mouth, and more especially the 
Spirochaetes. And here again I found—this time to my amaze- 
ment—that all these organisms also had first been seen and 
described by Leeuwenhoek. It seemed impossible ; so again I 
attempted to ascertain who this person really was, and what 
precisely he had discovered in this connexion. But I failed 
once more. 

Somewhat later, I turned my attention particularly to the 
intestinal protozoa of man—only to find that thevr first observer 
was, incredible though it seemed, again Leeuwenhoek. : 
To make a long story short, I continually found that whatever 
protozoa or bacteria I worked at, I was always forestalled and 
led back to the same mysterious and eluswe indiwidual who had 
somehow succeeded in registering the first observations on almost 
every kind of microbe I attempted to investigate. 

It is now some 25 years since I first began to try and find 
out something about Leeuwenhoek and his discoveries in proto- 
zoology and bacteriology. The task has always been hard, but 
because of my personal interest it has never been irksome. My 
interest has, indeed, grown with my knowledge; and the more 
I have found out, the more I have ever wanted to find out about 
this truly marvellous man and his works. From the very 
beginning, I have been able to get little or no help from the 
writings of others (most of whom merely led me astray), so that 
I have always had to do the best I could for myself. Conse- 
quently, the first few years of my labours were woefully barren : 
they yielded me little else than imperfect copies of Leeuwenhoek's 
publications in Latin, and their garbled English version—the 
“Select Works” of Hoole. As I soon detected the shortcomings 
(also the merits) of the latter, I applied myself at first to the 
study of the “ original” Latin texts. 

Thad barely begun to read the Latin letters of Leeuwenhoek, 
however, when I met with a serious setback. I found that 
these letters were not written in the Latin which I learnt at 
school, but in a language I could scarcely wunderstand—a 
language bristling with difficulties for a man like myself, whose 
‘“ Latin” was little more than a fading recollection of the 
dialect used by writers of the Augustan age. Yet long before 
I had mastered Leeuwenhoekian Latin I received a far worse 
shock: I discovered that Leeuwenhoek himself knew no Latin 
at all (of any kind or sort), and that all his own writings were 
really in Dutch. Profoundly discowraged, I therefore began a 
new search for the Dutch originals. 


When I finally succeeded in obtaining a copy of the Dutch 
edition of Leeuwenhoek’s works, 7¢ was only to find that I 
could make out hardly anything of what he had written: for 
af the instructors of my youth had taught me a Latin in- 
adequate to my needs, they had never even pretended to teach 
me one single word of the languages spoken in the Netherlands. 
So I made a foolhardy attempt to learn Dutch by myself— 
using Leeuwenhoek’s printed Dutch letters as a text, and 
checking my interpretations by the Latin editions of the same 
letters and the old Dutch Bible. When JI had made some little 
progress in this study, and had got a smattering of seventeenth- 
century Dutch and Latin, I made the worst (and the best) 
discovery of all: I discovered that Leeuwenhoek’s own original 
Dutch letters—written by his very own hand, and many of 
them even now unpublished—are still, for the most part, extant 
among the manuscripts belonging to the Royal Society in 
London. I therefore went, all excited, to consult them 
and found that nearly all those most important for my purpose 
were inscribed in a script which, for all I could make of tt, 
might just as well have been Hebrew or Arabic. I could not 
read a single word. 

This was a blow which staggered me completely: and as we 
were then in the midst of the Great War, and my time was 
more than fully occupied with other and more urgent duties, I 
momentarily gave up all hope of ever being able to read 
Leeuwenhoek in the original. 

But after the War, when my own work was temporarily at 
a standstill, I returned one day—‘ merely out of curiosity” (as 
he would say)—to the library of the Royal Society, and puzzled 
over those tantalizing manuscripts. After a bit, I found that 
I could make out a word here and there: in a few days I could 
even read, now and then, a whole sentence. So I became— 
almost unconsciously—an amateur palaeographer, and at last 
attempted to find and decipher and copy all the passages which 
specially interested me in Leeuwenhoek’s letters. T'o an un- 
prepared and wholly inexperienced person like myself it was a 
task nearly as great as that which faced the first readers of the 
Rosetta Stone, and it was accomplished by similar methods. 
You may laugh, dear Reader, but it is true. You, who are 
doubtless familiar with Dutch and Latin and English of all 
periods, and for whom the deciphering of ancient manuscripts 
holds no terrors, must please try to put yourself in my ignorant 


position and consider my handicaps. I knew—to my shame 
and sorrow—little Latin, less Dutch, and not much more 
Finglish of Leeuwenhoek’s time. I had nobody to help me, 
and therefore made the most pitiable mistakes. But I perse- 
vered, and ultimately attained my object (more or less). I also 
learnt afresh the truth contained in the Dutch-Latin proverb 
nil volentibus arduum—or, as we say in English, ‘‘ where 
there’s a will there’s a way.” 

When I had finally discovered where to look for Leeuwen- 
hoek, my serious work began. Having possessed myself—after 
long search and many bitter disappointments—of perfect copies 
of the Dutch and Latin editions of his writings, and with all 
the Royal Society’s manuscripts and Transactions available 
for study, I began my real hunt for the man himself and his 
protozoological and bacteriological knowledge. Whilst reading 
the various versions of his numerous letters, in quest of passages 
relating to protozoa and bacteria, I learnt much about himself 
and his multifarious other activities. In addition, naturally, 
I ransacked every accessible book and paper and manuscript 
for further information. And at last, after encountering 
obstacles at every turn, and surmounting difficulties which often 
seemed at first insuperable, I met Mynheer Antony van 
Leeuwenhoek his very self; and he told me all—or nearly all— 
that he knew about the Protozoa and the Bacteria. To my 
surprise and delight I found not only that he knew no language 
but Dutch, but also that he knew no “ science”; for he was 
merely an ordinary shopkeeper, holding a few minor municipal 
appointments, in the little old town of Delft. In the world of 
science he was no better than an ignorant and bungling 
amateur—self-taught but otherwise uneducated. He did every- 
thing by himself, alone and unaided: so that when he wished 
to make a microscopical discovery, he had first to make himself 
a nucroscope; and when he wished to describe this discovery, vt 
often turned out to be something so novel that he had no words 
wherewith to express it. Consequently, though we both strove 
hard, I often found it very difficult to understand what he kept 
trying to tell me: for he was terribly short of words, and could 
only talk in the commonest and most ungrammatical and old- 
fashioned language—often using expressions which are not in 
any modern Dutch-English dictionary (or if they are, have now 
a different meaning). How such a man ever became famous as 
a “scientist,” and even a Fellow of the Royal Society of 
London, is a curious story which I shall retell you presently. 


My own chief interest in Leeuwenhoek has always been in 
his observations on protozoa and bacteria—as I have already 
told you. But this is because these “ little animals’ (as he 
called them) have engaged my own attention all my life, being 
the favourite objects of my own researches. His own tastes 
were more catholic : indeed, he studied almost everything that 
can be looked at through a lens, and thereby found out some- 
thing new about it too. His inquisitiveness was insatiable, and 
his discovery of the Protozoa and the Bacteria was merely an 
incident in a life crowded with discovertes—real and imaginary. 
For example, Leeuwenhoek’s observations on insects, rotifers, 
and a host of other ‘‘animalcules,”’ are equally remarkable ; 
his researches on blood-corpuscles and the capillary circulation 
are already classics; his comparative studies of spermatozoa 
now stand as a landmark in the History of Biology; his dis- 
covery of parthenogenesis (in aphids) and of budding im an 
animal (Hydra) are too notorious almost for comment : while 
his other investigations in anatomy, histology, physiology, em- 
bryology, zoology, botany, chemistry, crystallography, and 
physics, only await editors for their proper appreciation. He 
made the maddest experiments, and attempted to see things that 
nobody would now even dream of seeing. I imagine, for instance, 
that nobody before (or after) Leeuwenhoek ever thought of 
watching the explosion of gunpowder under the microscope - yet 
he devised an apparatus for this purpose, and though he nearly 
blinded himself he succeeded in seeing what he wanted. And 
he actually discovered protozoa and bacteria in organic infusions 
in the course of a crazy attempt to find out, by the microscopic 
examination of macerated peppercorns, why pepper ts hot ! 

But these are only a few of Leeuwenhoek’s astonishing 
doings, and I need say nothing further about them here. In 
the pages which follow I merely attempt to assemble and edit 
all his observations on protozoa and bacteria. Originally I 
collected—simply for my own information and pleasure—every- 
thing that I could find on these matters, both published and 
unpublished, in his extant writings. I had no thought of 
making a book for others to read. Yet after a time I found 
that I had amassed a body of records which seemed to me so 
surprisingly great and original, that I felt it my duty to share 
my findings with other protozoologists and bacteriologists : so 
my own private notes gradually grew into the work now before 


At first I thought merely to print or reprint all the relevant 
passages 1n Leeuwenhoek’s writings in the languages (Dutch, 
Latin, or English) in which they now survive: but on second 
thoughts I realized that this would be futile. I realized that it 
would be useless, for example, to reprint the Dutch and Latin 
words already accessible to everybody, and by everybody still 
unread or misunderstood. So I resolved to put everything into 
Finglish, in order that every man who can read my mother- 
tongue shall henceforth be able to read and understand what 
Leeuwenhoek himself recorded in his own language. My 
translations of his words are, I know, imperfect : but they are 
to be excused as a first attempt to reduce all his protozoological 
and bacteriological knowledge to a uniform and intelligible 
modern system, and vn every case they are accompanied by exact 
references to original sources, so that you can—if you have the 
time and patience—verify my own words for yourself. A certain 
amount of editing and rearrangement has been unavoidable, 
and indeed essential to my plan; but I have, I hope, reduced 
my apparatus criticus to a minimum. 

The difficulties which I have encountered in translating 
Leeuwenhoek into modern English—or, at least, into English 
sufficiently modern to be nowadays intelligible—have been very 
great. I could have rendered his words much more easily in 
the English of his own period—interlarded as it was with 
Capitals and wtalics and irregular and curious spellings and 
the queerest punctuation. But this, while superficially pre- 
senting an old-world appearance, would have been nowise 
satesfactory to You, dear modern Reader. Rather would it 
have recalled the false ancientry of William Morris, whose 
“Old English” was often no better than anachronism: for I 
emagine that many of Morris’s “ translations” —such as his 
version of Beowulf—are written in a language which no other 
Englishman ever employed. They remind me unpleasantly of 
“Ye Olde Englishe Petrole Pumpe,” from which (I am told) 
motorists can now fill their tanks within 20 miles of London 

All my translations of Leeuwenhoek (as you will soon ob- 
serve) are compromises between ancient and modern. I adopt 
old words and old phrases (used by his own English contempor- 
aries) whenever they are understandable at the present day, but 
I eschew—on principle—all unfamiliar expressions. I want 
you, dear English Reader, to read Leeuwenhoek in his own 


words—as nearly as possible—but above all I want you to 
understand him; and I do not forget the warning issued to the 
translators of the Targums (the Aramaic versions of the old 
Hebrew testament): “He who translates quite literally is a 
liar, while he who adds anything is a blasphemer.” The Rev. 
Dr Pusey hit the nail on the head, I think, when he said (in- 
troducing his English rendering of St Augustine) that a 
translation of an author should be “a re-production’ in another 
language, ‘with as little sacrifice as may be of what is peculiar 
to him”: adding feelingly that “it is very difficult to avoid 
introducing some slight shade of meaning, which may not be 
contained in the original.” This, and more than this, I dis- 
covered for myself many years ago. Long ago I realized the 
truth of the Italian saying “ traduttore traditore ”—a trans- 
lator is no better than a traitor. Instinctively I dislike and 
distrust translations, and it is only by the trony of fate that I 
now appear before you in the garb of a translator myself. I 
would also add, in the words of another interpreter of St 
Augustine (the Rev. Marcus Dods): “That the present trans- 
lation also might be improved, we know; that many men were 
fitter for the task, on the score of scholarship, we are very 
sensible ; but that anyone would have executed it with intenser 
affection and veneration for the author, we are not prepared to 

In making my translations for you I have always tried— 
with what success you must judge—to preserve the flavour of 
Leeuwenhoek’s own writings, yet at the same time to satisfy 
the requirements of the most up-to-date protistologist : and 
when I have had to translate the words of other authors, or of 
old documents, I have always tried to preserve their individual 
peculiarities in a like manner. My ideal has not (I know) been 
attained, but it is probably unattainable : nevertheless, you will 
(I hope) perhaps allow me some small credit for possessing, in 
these uninspired times, even an ideal, towards which I have 
ever striven. No similar attempt has ever been made by 
another—despite its crying need. No protozoologist or bactert- 
ologist has ever before so much as read, or even pretended to 
read, all Leeuwenhoek’s extant writings on these subjects ; and 
those authors who have previously offered to interpret his dis- 
coveries have usually gone ludicrously astray themselves (whereof 
I shall give you many instances). Almost everything that has 
yet been written about Leeuwenhoek’s work on protozoa and 


bacteria is glaringly inaccurate. His fame has consequently 
suffered, though the reputations of his translators and traducers 
are bound to suffer far more in the end. If I succeed only in 
showing you his own immeasurable superiority over all his 
commentators (including, of course, myself), my work will not 
have been wholly wasted. 

And now, dear Reader, after prejudicing my case with these 
disparaging remarks, Imust cast myself wpon your mercy. I 
am forced to confess that, had I fully understood the difficulties 
of my present undertaking at the outset, I would never have 
embarked upon it: for it is a work suited to a linguist, his- 
torian, antiquary, and man of leisure, and unhappily I possess 
none of these necessary qualifications. The only qualification 
which I can justly claim is that I have spent all my time and 
energies, all my life, in studying the micro-organisms which 
Leeuwenhoek discovered ; and consequently I imagine that I 
know the subject-matter of his writings on protozoa and bacteria 
as no mere scholar or philologist can ever hope to know it. I 
freely admit that my knowledge of Dutch, Latin, Greek, French, 
German, Italian, and even English, is unscholarly and defective : 
but I venture to assert that nobody, however skilled he may be 
in these tongues, can ever comprehend Leeuwenhoek’s writings 
on protozoology and bacteriology unless he be himself a working 
protozoologist and bacteriologist. And this I conceive to be the 
primary and indispensable qualification for anybody who would 
rightly interpret his discoveries in these disciplines. But no 
man can do everything : and a modern protozoologist has little 
time for studying the classics or for learning languages. He 
has not even time to read all the current literature on his own 
subject. I can but plead, therefore, that my knowledge of 
Dutch and Latin and English would (I hope) have been greater 
uf Thad not applied all my chief energies, all day and every 
day, to the practical study of protozoa and bacteria. The study 
of Leeuwenhoek ?s really an occupation—to use his own words— 
“for a whole man, which my circumstances did not allow of : 
and I have devoted only my spare time to rt”. 

Yet very seldom, dear Reader, in the course of my working 
life have I had anything that you could fairly call “ spare time”. 
For many years I have had to work for seven days in every week 
and for fifty weeks in every year at my own researches : conse- 
quently, I have had little opportunity to edit Leeuwenhoek’s— 
or even to read his voluminous writings. Most of the lines 


which I now offer for your indulgent perusal have been written 
at odd moments in the course of other studies of my own. 
Weeks, months, and even years, have often elapsed between sen- 
tences and paragraphs which now run consecutively in the 
following pages—long periods filled with most concentrated 
work on subjects but distantly related. I beg you, therefore, to 
bear this ever an mind, but especially when you detect inconsts- 
tencies (whereof there are, I fear, many) in the several sections 
of this book. it has been some 20 years a-writing, and I am 
not now the same person that I was 20 years ago. 

If you are disposed (which is like enough) to find fault with 
my poor scholarship, Iintreat you to consider kindly what I 
have already published of my own researches (which ws but a 
small fraction of what I have done), and to remember that the 
present publication of Leeuwenhoek’s work has been an addi- 
tional charge upon these my own most exacting labours. The 
whole of this book has been written at irregular intervals and 
under very great difficulties—mostly at the dead of night 
(between midnight and 8 a.m.) after a hard day’s work at my 
own researches, and with another similar day in the laboratory 
before me. IPf you find that I have done my task badly, please 
remember that it has been almost impossible for me to do vt at 
all. Icannot even tell you now how I have achieved it: but 
to show you the shifts to which I have been put wm order to 
carry out this undertaking, however wll, I may tell you that one 
of the following translations (and that, I think, not the worst) 
was made during several long and interrupted nights im the 
Great War, when German airplanes were trying to drop their 
bombs on London. Any one of these random missiles might 
well have fallen upon Burlington House and utterly destroyed 
all Weeuwenhoek’s priceless original letters (not to mention 
myself). . . . But he said himself prophetically that he 
“never trusted people, especially Germans”; though he also 
said more generously elsewhere, in another connexion, “ yet 
theyre to be forgiven, for they know no better”’. 

I know that I cannot paint you a true picture of Leeuwen- 
hoek’s protozoology and bacteriology without framing it with 
some authentic account of himself. This also I have therefore 
attempted. But almost every veridical record of his life ts 
buried in obscurity: almost every biographer of this great dis- 
coverer seems to have taken delight in burying his own findings 
in almost inaccessible places, where others could discover them 


only by chance or inspiration. Consequently, much still 
remains to be unearthed. I have only scraped the surface here 
and there—through lack of opportunity to delve more deeply— 
and must reluctantly leave the rest of the work to others. You 
will therefore please remember, dear Reader, that my present 
“life” of our great Delvenaar makes no pretence to be more 
than a preliminary collection of materials for the use of some 
more competent future historian. 

About Leeuwenhoek himself the greatest ignorance still 
prevails—not only in England but even in his native country. 
Only one full-length biography (by Haaxman) has yet been 
printed ; though Bovrtet, van Haastert, Halbertsma, Harting, 
and more recently Bouricius, Schierbeek, and others, have 
published many valuable data. ‘T'o Haaxman’s booklet all 
students will forever be deeply indebted: but none can swppose 
that the Rotterdam apothecary, writing more than half a 
century ago, was in a position to say the last word about 
Leeuwenhoek, or to appraise his scientific achievements at their 
true worth. Outside of Holland little has been written about 
him which is not almost comically inaccurate. The biographi- 
cal dictionaries are stuffed with ridiculous statements, and 
most historians of biology have hitherto been content to misprint 
their mistakes. 

Leeuwenhoek himself is, indeed, now almost unknown— 
notwithstanding his celebrity. If yow doubt wt, dear Reader, 
go to his native town of Delft, and make inquiries for yourself. 
Ask any man wm the street about him, and he will probably 
direct you to a modern road which now bears his name—a 
road outside the old town in which he lived, and leading to 
the railway station. Or your informant will possibly send you 
to a spot where a bronze effigy of our hero now hangs on the 
railings surrounding the playground of a girls school. “Here”’, 
you may read, ‘‘ Leeuwenhoek, the discoverer of the Infusoria, 
lived and worked in the year 1675 "—the year (presumably) of 
the discovery. Yet he never lived in that street, nor was the 
discovery made wn that year. The whole memorial is mistaken 
and misplaced. If you still doubt my words (when I say that 
Leeuwenhoek zs comparatively unknown, even to his own 
countrymen), let me tell you a story for whose truth I can 
vouch. A few years ago, a party of Dutch physicians visited 
the Institute where I work. One of them, on hearing from 
a colleague that I had been studying Leeuwenhoek’s letters, 


expressed a desire to meet me: and on being introduced he 
said “I am glad to make your acquaintance, as I also am 
interested in Leeuwenhoek; I understand that you knew hum 
personally ?”’. 

To appreciate Leeuwenhoek properly, it is (I submit) need- 
ful to know not only the particular history of many sciences but 
also the general history of his own times: and to see him in 
his true perspective it is even necessary to understand the 
relations of Holland and England in his day, and the peculiar 
circumstances which led to the founding of the Royal Society 
and to his connexion with that learned assembly. I confess 
I do not fully comprehend any of these things myself, so I can 
here do no more than indicate a few sources of my own imperfect 

Most men of my acquaintance seem to know little more of 
the history of Holland than is contained in those ever-popular 
English classics written by John Motley (an American), whose 
great stories end where Leeuwenhoek’s life begins. Yet 
Leeuwenhoek’s period is well documented on the English side : 
for it is covered by such deservedly famous and widely read 
records as the Diaries of gay Samuel Pepys and gentle John 
Evelyn ; John Ray’s unadventurous but instructive Travels ; 
dear Dorothy Osborne’s entrancing Letters to her future 
husband William Temple; the entertaining Epistles of the 
Welsh scholar James Howell; Gilbert Burnet’s solid History 
of his own Times ; and the indiscreet Scottish-French Memoirs 
of Count Grammont written by Anthony Hamilton. (I may 
perhaps remind you that Pepys, Evelyn, Ray, and Howell all 
travelled in Holland: that Sir William Temple was once our 
Ambassador at The Hague: and that Bishop Burnet not only 
lived in Holland but even married a Dutchwoman—of noble 
Scottish descent. Pepys, Evelyn, Ray, and Burnet were, as of 
course you know, once distinguished Fellows of the Royal 
Society.) What little I have been able to learn of life in 
England and Holland in Leeuwenhoek’s day has been derived 
from these and other contemporary writers, rather than from 
professional modern historians. Nevertheless, I have not 
neglected to study (I hope with profit) the excellent works of 
Motley and Edmundson and Bense and others, and the well- 
known Histories and Record of the Royal Society compiled 
by Sprat, Birch, Thomson, Weld, and the rest. I have even 
learned something from the scribblings of men like Ned Ward, 


the London publican and sinner, who left us the common mans 
view of the Royal Society and its Fellows at the time when 
Leeuwenhoek was in his prime. I regret that space will not 
allow me to quote at length Ned’s description of a typical 
Fellow of his period, who “could see as far into a millstone 
as another :” or of the Society’s musewm at “ Wiseacres’ Hall” 
[Gresham College|\—a “warehouse of Egyptian mummies, 
old musty skeletons, and other antiquated trumpery : 
skeletons of men, women and monkeys, birds, beasts, and 
fishes; abortives put up in pickle, and abundance of other 
memorandums of mortality.” 

Tempora mutantur, nos et mutamur in illis—the times are 
changed, and with them we ourselves. ’tis a hackneyed phrase, 
dear Reader, and as you know a misquotation, but none the less 
true. Today an Englishman must almost apologize for reintro- 
ducing an ancient Hollander to his own countrymen, and for 
presuming to revive und interpret his long-forgotten words. 
Yet England and Holland were once more closely goined—both 
geographically and spiritually. Only 250 years ago the links 
of language and spiritual endeavour needed no emphasis: vt 
would then even have been unnecessary to explain the manifest 
connextons between certain bits of Holland (such as Delft and 
Leeuwenhoek) and allied bits of England (such as London 
and its Royal Society). Today, alas! we are apt to forget 
our common heritage of race, language, religion, and even 
science. . . . The times are changed indeed. 

You will doubtless exclaim that I exaggerate the affinities 
between the Dutch and English nations: and you will (with 
some show of justice) oppose my statements with familiar argu- 
ments from certain memorable wars—both old and new. But 
please do not forget that those old contests for naval and 
colonial supremacy were fought in the days before we had 
learned to express our rwalry in the form of tennis and 
football: and if you should perchance remind me of South 
Africa, pray remember also that Christianity was originally 
implanted in Holland herself chiefly by monks from Britain, 
and that the struggle for religious freedom—and its ultimate 
success—ran sympathetically parallel in both countries. Hven 
when England and Holland were at war, Englishmen and 
Scotsmen (as you know) once fought on both sides against the 
common enemy : it was once no inconsistency, during an Anglo- 
Dutch war, for British troops to fight simultaneously side-by- 


side with Hollanders against Spain or France or Germany. 
You will remember too, I hope, that an English nobleman 
(Dudley, Earl of Leicester) was once Governor-General of 
Holland—after his mistress, our good Queen Hlizabeth, had 
been offered (and had refused) the sovereignty of the States. 
Had Cromwell’s dream—a little later—come true, Englishmen, 
Scotsmen, Irishmen, Welshmen, Hollanders, Zealanders, and 
Frieslanders, might even now be living together in the first 
“United States”. Just think of that! And of more personal 
and private relations, let me recall the beautiful friendship of 
Erasmus and Thomas More—a Dutchman and an Englishman 
who were true brothers. Let me remind you also that the first 
President of the Royal Society (Sir Robert Moray) was formerly 
a soldier in the Netherlands, where he had many friends, and 
could speak the language; that a very celebrated Hollander 
(Christiaan Huygens) was among the first Fellows; and that 
the Royal “ Patron and Founder” of our Society was himself 
an exile in Leeuwenhoek's land during his lifetime. 

But you will ask (very properly) what all this has got to do 
with Leeuwenhoek himself and with this book? I will tell you. 
In reintroducing plain Mr van Leeuwenhoek, the Dutch draper 
and amateur micrographer, I want also to vmpress upon you 
that there are still blood-brothers in every different nation. 
Barriers erected by birth and prejudice and education are 
blown sky-high before the fire of common human aims and 
interests. Language and land and lineage are no bars to 
mutual and native understanding. An honest man in any 
country is linked to all other honest men in all other countries. 
-_ When a true man like Antony van Leeuwenhoek ?¢s born, the 
heavens are opened. Even when he dies he is not dead: his 
spirit glows with the divine light forever, and will forever be 
seen and understood—somewhere, sometime, by somebody. No 
Princes, Popes, politicians, or even prophets, can unite man- 
kind in universal brotherhood; but the disinterested and simple 
men everywhere can (and perhaps eventually will) unknowingly 
draw warring nations together, and may ultimately save 
humanity from the fate of the Triassic reptiles. As surely as 
Leeuwenhoek, the old Dutch draper, has—after centuries of 
misunderstanding—established connexion with me, a modern 
English biologist, and has awakened my sympathy with himself 
and his countrymen; just as surely will other men of other 
nations and other interests be drawn together by the endearment 


engendered by common enterprise and common human endeavour. 
This is the real League of Nations—the only one that can ever 
succeed or survive. 

Therefore, dear Reader, meet Mr van Leeuwenhoek (a 
simple and ordinary dead Dutchman) and shake him by the 
hand and hearken to what he has to say. When you have 
done that, you will not only know the true meaning of that 
misused term “ scientific research”, but you will also realize 
(I hope) that you have already gone further along the path of 
peace and progress than some of the more sophisticated people 
now sitting solemnly at Geneva or at the meetings of the most 
learned and modern and Royal and scientific societies (God 
bless and prosper them all!). 

For my own part, I will only add—though it must now 
be obvious—that the making of this book has been to me a 
labour of love: and as such it is offered with all its manifest 
imperfections to You, good Reader, and to all other lovers of 
Leeuwenhoek and of his “little animals” and of all else 
that such love implies. 




Philips v. Leeuwenhoek married Margriete Bel v.d. Berch 

Their son Antony van Leeuwenhoek born at Delft 
Father buried 
Mother remarried 
Apprenticed to draper in Amsterdam 
Draper and haberdasher in Delft . 
Married Barbara de Meij 
Maria his daughter born 
Appointed Sheriffs’ Chamberlain of Delft 
Mother buried : 
First wife (Barbara) died 
Appointed Surveyor 
Married Cornelia Swalmius . : 
Addressed first letter to Royal see of London 
Discovered the Protozoa 
and the Bacteria 
Executor of Vermeer’s estate 
Wine-gauger of Delft 
Fellow of the Royal Society 

Second wife (Cornelia) buried 
Correspondant de l Académie des Sciences, Paris 
Died at Delft 
and buried in the Ola Chasen 
Tomb erected 
Maria died 

Microscopes sold . 

30 Jan. 1622 
24 Oct. 1632 
4 Nov. 1632 
8 Jan. 1638 

18 Dec. 1540 

circa 1654 

29 July 1654 

. 22 Sept. 1656 

26 Mar. 1660 
3 Sept. 1664 
11 July 1666 
4 Feb. 1669 
25 Jan. 1671 © 
Apr. 1673 


. 380 Sept. 1676 

15 Aug. 1679 

29 Jan. 1679/80 O.S. 
= 8 Feb. 1680 N.S. ] 

6 Jan. 1694 
4 Mar. 1699 
26 Aug. 1723 
31 Aug. 1723 
: 1739 
25 Apr. 1745 
29 May 1747 



A very civil complesant man, & douptless 
of great natural Abileties; but contrary 
to my Expectations quite a stranger to 
letters, .. . which is a great hindrance 
to him in his reasonings uppon his Obser- 
vations, for being ignorant of all other 
Mens thoughts, he is wholy trusting to 
his own.—Dr Thomas Molyneux (1685). 



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NTONY VAN LEEUWENHOEK,’ the hero of the 

A following pages, was born at Delft in Holland on 

24 October 1632. He died in his native town on 

26 August 1723; being then aged—as his epitaph informs 

us, with appropriate numerical particularity—‘ 90 years, 
10 months, and 2 days.” 

The year of Leeuwenhoek’s birth is memorable, to 
Englishmen and Hollanders alike, as that in which several of 
our other great men—of widely different genius—were also 
born: our philosophers John Locke (1632—1704) and Baruch 
de Spinoza (1632—1677); the architect Christopher Wren 
(1632—1723); and the famous painters Jan Vermeer of Delft 
(1632—1675) and Nicolaes Maes (1632—1693). It is also 
remembered by historians as the year of the Siege of 
Maestricht, which marks approximately the middle of the 
Thirty Years’ War. The unhappy Charles I was then King 
of England; the great Prince of Orange Frederik Hendrik, 
whose period is called a “golden age”’ by Dutch writers, was 
Stadholder of the United Netherlands: and for both Holland 
and HKngland the times were big with coming developments in 
politics, religion, and commerce—no less than in science, 
philosophy, and art. Verily astrange hour for the birth of one 
who, while leading in the midst of wars the peaceful life of a 
provincial tradesman, was to win immortal fame by his amateur 
activities as a man of science. 

Of Leeuwenhoek’s parents not much is certainly known. 
His father was named Philips Antonysz. van Leeuwenhoek’, 

* For orthography, derivation, and pronunciation of the name, see 
p. 300. 

* 7.e., Phillip, son of Antony v. L. The name is sometimes given as 

Philips (or Philippus) Antony, but this is a mistake. Of. Boitet (1729), 
Haaxman (1875), and Soutendam (1875). In an old genealogical tree— 
which I have seen—in the possession of the Haaxman family, the name is 
written as given above: but in the archives of Delft he is styled simply 
“Philips Thonisz.” (Bouricius, 1924, 1925.) 


and was a basket-maker living in the East-End (Oosteinde) of 
Delft—near the now long-vanished TLeeuwenpoort’. He 
appears to have been a craftsman of good Dutch stock, but of 
no personal or social distinction. His own father (Antony 
Philipszn.) was likewise a basket-maker *. 

Leeuwenhoek’s mother was Margaretha, daughter of Jacob 
Sebastiaanszoon Bel van den Berch’, a Delft brewer*. She 
belonged to a good family, and was related to other Dutch 
families of equally good standing’. The brewers then, as now, 
were no inconsiderable folk in Holland; and it thus seems 
clear that any claims which our Antony may have to gentle 
birth must rest upon his mother’. 

Philips van Leeuwenhoek and Margaretha Bel van den 
Berch were married in 1622. Their betrothal (ondertroww) 
was formally announced on January 15, and the marriage took 
place on the 30th of the same month—as Bouricius has now 

‘ Cf. p. 338 sq., infra. The house in which he is believed to have 
lived, and in which L. was born, is shown in Plate II. 

® fide Bouricius. The Leeuwenhoeks, for several generations at least, 
were consistently named Phillip and Antony alternately. (Cf. the family 
tree, p. 18.) This system of alternate nomenclature seems to have been 
common in Dutch families at that period. (L. himself made three unsuccess- 
ful a to rear a son called Phillip—as will be evident in the family 

* alias Berg, or Bergh. The name is spelled variously. Margaretha’s 
forename is also given as Margriete (cf. Schierbeek, 1930) and Grietge (cf. 
Plate III). 

* Cf. Boitet (1729), Soutendam (1875), Haaxman (1875), and Bouricius 
(1924, 1925). lL. himself tells us (Send-brief XXII, 16 May 1716) that his 
grandfather and great-grandfather were brewers, and that his grandmother 
was the daughter of a brewer. But his grandfather on the father’s side 
(another Antony) was, as just noted, only a basket-maker. 

* Namely, the families of Hoogenhouk, Bleiswijk, Swalmius, and 
Mathenesse. Cf. Boitet (1729), Halbertsma (1843), and Haaxman (1875). 

® Boitet (1729), only six years after L.’s death, records that he came 
from ‘‘zeer deftige en eerlyke ouders’’; but this was perhaps merely a 
euphemistic way of saying that he was born of respectable parents. It can 
hardly be taken to prove that he belonged to the aristocracy. Although it 
would be unusual to call a basket-maker “ zeer deftig”’ at the present day, 
such hyperbolic expressions were as customary in Holland as they were in 
England at the date when Boitet’s book was published. It must be 
remembered, also, that his book was not issued with the object of belittling 
Delft and her burghers. 



in the East-End (Oosteinde) of Delft: as it appeared in November, 1926. 
[Identified by Mr L. G. N. Bouricius. Now demolished. | 

facing p. 20 

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facing p. 21 


ascertained definitively. Antony, their first son and fifth 
child, was born to them ten years later. He was born on 
24 October, and was baptized in the New Church at Delft on 
4 November’, a.D. 1632. (See Plate IIT.) 

It is recorded that Antony had four® surviving sisters— 
Margriete, Geertruyt, Neeltge, and Catharina—though very 
little is now known about any of them. We know,‘ however, 
that Margriete [Margaret] the eldest (born 1623), married one 
Jan Molijn,’ and herself bore five children; and one of these, 
named Maria (like Leeuwenhoek’s own daughter), married 
a certain Cornelis Haaxman from whom Leeuwenhoek’s 
biographer, P. J. Haaxman, claimed descent. Geertruyt 
[Gertrude] was born in 1626, and Catharina in 1637°, and 

1 See Bouricius (1924, 1925). The date ‘5/30 Jan.” given by Schier- 
beek (1980) is incorrect, and should read “ 15/30.”—It has recently been 
alleged by Naber that L.’s father had previously tried to marry one of the 
daughters of the adventurer Cornelis Drebbel (1572—1633), who is 
regarded by some admirers as the inventor of the microscope. Naber even 
avers (p.32) that L.'s father was ‘‘one of Drebbel’s lens-grinders”; and 
would insinuate apparently that what L. himself knew about lenses was 
learned from his father, who in turn derived it from Drebbel. But this 
story is apocryphal. We now know that L.’s father was not a lens-grinder 
but a basket-maker, and that he died when Antony was only 5 years old: 
and we now know also—thanks largely to Jaeger (1922)—a good deal about 
Drebbel. Dr Schierbeek, who first drew my attention to Dr Naber’s 
statements, wrote to ask for his evidence: and as a result of this correspon- 
dence (which Dr Schierbeek kindly allowed me to read) and of my own 
inquiries, I can only conclude that no evidence exists. Cf. Jaeger (1922, 
especially p. 7) and Bouricius (1924). 

* Schierbeek (1923), Bouricius (1924, 1925). Schierbeek (1930), through 
a misprint, wrongly gives the date of baptism as Nov. 14. 

* Haaxman (1875), Schierbeek (1930). Two other children—a sister 
(Maria) and a brother (Jacob)—died in infancy. Haaxman mentions only 
3 sisters, but Bouricius has since discovered the existence of the fourth 
(Neeltge), who apparently attained maturity. The names of Margriete and 
Geertruyt are spelled ‘ Margaretha” and “‘Geertruida”’ by Haaxman. 

* Haaxman (1875), Bouricius (1924). 

* This Jan Molijn (alias du Molyn), who married L.’s sister Margaret 
on 10 May 1643, was himself the son—by an earlier marriage—of the 
Jacob Molijn whom L.’s mother (also named Margaret) married after the 
death of her first husband (L.’s father): fide Bouricius, in litt. 

° According to Bouricius (1924) and Schierbeek (1930).—Catharina, who 
was married to Claes Jansz. van Leeuwen in 1655, is referred to by L. 
himself in unpublished postscripts to Letter 13a (22 Jan. 1676) and 
Letter 39 (17 Sept. 1683), in both of which he requests that the Phil. Trans. 


both married subsequently. Neeltge | Nellie] apparently died 
young. (See the Family Tree, p. 18.) 

All the trustworthy evidence now available thus shows 
that Antony was a true Hollander of decent though not of 
aristocratic descent—a child of fairly well-to-do tradespeople. 
Richardson’s statement (1885)—unhesitatingly accepted by 
Locy (1901, 1910), Plimmer (1913), and others—that he was 
of ‘ Jewish Saxon ” extraction, is nothing but a wild specu- 
lation’: and the evidence against the guess that Leeuwenhoek 
was a Jew, or of Jewish origin, is overwhelming. Mr Bouricius 
assures me’ that “‘there were practically no Jews in Delft” 
at that date: and if there were any, they certainly did not 
then engage in basket-making or in brewing, nor did they hold 
any municipal appointments (from which they were debarred). 
Moreover, the baptisms and marriages and burials of all 
members of the families concerned (whose names are obviously 
not Jewish) were entered in the registers of the Reformed 
Church; while Leeuwenhoek was, of course, himself baptized 
in the New Church and buried in the Old Church at Delft. 
Mr Bouricius, who speaks with authority, says: “In geen 
geval was van Leewwenhoek een jood’’—Leeuwenhoek was no 
Jew anyway. 

When our Antony was only five years old, his father Philips 
died,’ leaving his mother in sole charge of their little family. 
But soon afterwards (18 December 1640) she married again— 
her second husband, Antony’s stepfather, being a painter 
named Jacob Jansz. Molijn, who died in 1648. Antony’s 
mother herself died 16 years later, and was buried in the Old 
Church at Delft on 3 September 1664.’ 

may be forwarded to him through “ Mistress Catharine Leeuwenhoek, 
widow . . . living in the High Street at Rotterdam.’ She had no 
children (fide Bouricius). : 

' Richardson’s ridiculous statement had no other foundation than his 
own imagination. The “Jewish” and “ Saxon’”’ ancestors were divined by 
inspection of L.’s portrait ! 

* in litteris. 

* He was buried in the Old Church at Delft on 8 January 1638 
(Bouricius, 1924). The exact date of his death I have been unable to 
ascertain. Of. Schierbeek (1930). 

“ The foregoing facts—imperfectly noted by earlier biographers—are 
recorded in part by Bouricius (1924, 1925), and additional confirmatory 
details have been kindly sent me by him in personal communications. Cf. 
also Schierbeek (1929, 1930). 


Somewhere about the time of her second marriage, Antony’s 
mother put him to school at Warmond, a townlet a few miles 
north of Leyden. After receiving his earliest education here, 
he went—at what age is not exactly known—to live with an 
uncle who was an attorney, and also town clerk, at Benthuizen.’ 
It has been said that young Antony was at this time con- 
templating a similar career, and that he went to his uncle to 
prepare himself for it.” But there appears to be very little 
foundation for such a supposition ; and it has been judiciously 
remarked * that, as he was never even taught Latin, it is un- 
likely he was ever destined either for the law or for the 

But whatever his own or his family’s intentions may have 
been at this date, we know certainly that Antony neither 
progressed far in the study of the law nor did he prepare himself 
for a university career. We may suppose, however, that his 
education was not wholly neglected during his residence with 
his uncle: and it was, perhaps, at this time that he acquired 
those rudiments of mathematics and physical science in which 
he so delighted to indulge himself in his later life. Yet it is 
certain that he received no instruction in languages, for to the 
end of his days he knew none but his own.* 

In 1648° (the year in which his stepfather died) Antony, 
being 16 years of age, was sent to Amsterdam—then, as now, 
one of the great commercial cities of the world. He was there 
placed in a linen-draper’s shop, in order to learn the business ; 
and in a very short time he qualified himself as a draper and 
rose to the position of book-keeper and cashier’—a post which 
he held for several years at least. How long he remained in 
the shop at Amsterdam is not known, and nothing is known 
with certainty regarding his other doings at this period. But 
it seems probable that during his sojourn in the capital he 

’ Cf. Boitet (1729) and Haaxman (1875).—Benthuizen is a small place 
some 9 miles N.H. of Delft. 

* Boitet (1729), followed by v. Haastert (1823). 

* Halbertsma (1843). 

* Of. p. 305 infra. 

° Schierbeek (1929) gives the year as 1638: but this is obviously a 

° According to Boitet (1729), who is copied by later biographers. There 
are no known records extant relating to L.’s apprenticeship. 


made the acquaintance of Swammerdam,’ and perhaps of other 
young men with congenial interests. 

I may remind the reader that in 1648—the year in which 
Antony went to serve in the shop at Amsterdam—the Treaty 
of Minster, which ended the Thirty Years’ War, was signed. 
This reminder will recall the posture of Kurope at the moment 
—a moment when “ Holland had taken her place in the very 
front rank in the civilised world, as the home of letters, science 
and art, and was undoubtedly the most learned state in 
Kurope.” ° 

About six years after his first apprenticeship in Amsterdam, 
Leeuwenhoek returned to his native town: and here, for the 
rest of his days, he remained. For nearly 70 years—from 
1654 until the day of his death in 1723—he lived and worked 
in Delft; so that when, in the fullness of time, he became 
famous, he also became enduringly identified with his 
habitation. During his later lifetime he was regarded as one o 
the sights of the place—hardly less conspicuous than the Old 
Church, and almost as permanent a fixture. 

As Delft forms the background of all the scenes displayed 
in this book, I must here say a little more about this fine old 
town. ‘There are several descriptions and many pictures of 
the place as it was in Leeuwenhoek’s day. We have, for 
example, not only the compendious and valuable Dutch 
accounts by Dirk van Bleyswijck (1667) and Reinier Boitet 
(1729)—enriched with numerous engravings—but also various 
shorter and less particular records contained in works such as 
the earlier Latin “ Batavia” of Junius (1588) and “ Batavia 
Illustrata”’ of Scriverius (1609), and in the anonymous but 
once popular French guide-book called “Les Délices de la 

* That L. was acquainted with Swammerdam we know from his own 
statements (e.g., he refers to visits which Swammerdam paid him in Letter 6, 
7 Sept. 1674). Haaxman has gone so far as to suggest (1875, p. 10 seq.) 
that it was Swammerdam who, during L.’s residence in Amsterdam, first 
aroused his interest in microscopic studies. But this appears improbable: 
for, as Pijzel (1875, p. 108) points out, Swammerdam was only 11 years old 
when L. went there, and not more than 16 or 17 when he left: and we can 
hardly suppose, therefore, that L. received much guidance from so youthful 
and junior a mentor. 

* Edmundson (1922), p. 186. This is an indisputable fact which many 
people nowadays—in many different countries—are all too apt to forget. 

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facing p. 25 



On the left, the 

the distance, the tower of the Old Church. 

the main thoroughfare of the town, looking northwards. 


East-India Company’s house 
From an old engraving. 


Hollande.”* All old histories of Holland and of the House 
of Orange” also contain repeated references to Delft—the 
family’s stronghold in the Netherlands. Here William the 
Silent was assassinated (you can still see the hole made by the 
murderer’s bullet in the wall of the staircase of the Prince’s 
Court): and here, in the New Church, is the mausoleum 
wherein many of the most distinguished sons and daughters 
of the House lie buried. Delft, in the time of Leeuwenhoek, 
also forms the subject of one of the world’s pictorial master- 
pieces.” But the best and shortest description of the town at 
the time when Leeuwenhoek was in his prime—when Holland 
and England were at settled peace under William III of 
Orange and Great Britain—is, I think, that left to us by an 
obscure Englishman, William Mountague, Hsq., who once 
spent a holiday in Holland and afterwards wrote a lively 
description of what he saw. From his little book (1696) I 
may quote the following lines*: 

Delftis a fair and populous City, very clean, well built, 
and very pleasant; well seated in a Plain of Meadows, 
which may be laid all round under Water, if they open 
their Sluces, when the Wind is Kast-North-EHast. At 
the Entrance of it stands a general Magazine of Warlike 
Stores (but no Powder’) for the Publick Service. This 
City was burnt to Ashes Anno 15386, but soon re-built, and 
now in greater Glory than ever. The Hast-India Com- 
pany of this Place have here a very good House and large 
Ware-Houses; as also an eighth part of the Great or 
General Stock, this being the Third Town of Holland, 
having the Third Voice in the States, whither it sends 
Deputies, as also to all the other Colleges. Here are very 

' Pepys (Diary, 10 Dec. 1663) mentions that he bought a copy of this 
work. I have read only the revised version of 1710. 

* As examples I may mention the early Dutch histories of William 
and Maurice (see Anonymus, 1662), and the Historia Nostri Temporis by 
Brachelius (1666). 

® See Plate VII, opp. p. 35. My small reproduction gives but a poor 
idea of the splendour of the original painting. 

“ Mountague (1696), p. 18 sq. 
° Cf. footnote 3 on p. 55 infra. 


fine Buildings, and amongst them the Town-House,' with 
these two Verses on the Front. 
Haec domus odit, amat, punit, conservat, honorat, 
Nequitiam, Pacem, Crimina, Jura, Probos. 

Here is a spacious Market-Place between this House 
and the great Church,’ in which stands William‘ the 
First Prince of Orange (Great Grand-Father to his Sacred 
Majesty King William’) at full length, in Armor, in 
Copper Effigie . . . ’Tis the most Magnificent Tomb 
in all the Seventeen Provinces. Here that Prince kept 
his Court, and here was that brave Prince assassinated in 
the 5lst Year of his Age .. . 

In the t’other Church’ is a Monument of Admiral 
Trump’s' inrich’d with Miniature, and a fine Inscription 

In the same Church is Myn Heer Pithin’s Tomb‘, 
a very handsome one. . . . The Churches here, and in all 
the Seven United-Provinces, are generally bigger than ours 
in Hngland, but fewer in Number. 

Here is a large and neat Market, or Flesh-Hall (as they 
call it) for all sorts of Butchers Meat, which they have 
very good . . . They have also a good Fish-Market 
here, and another of Fruits, Roots, and Herbs. 

The People in this City are rich, trade much to Sea, and 
make much Porcelain, or fine Earthen Wares, to a great 
Perfection, tho’ far short of China, which they pretend to 
resemble, and brew good Beer here . . . yet it tastes 

" The Stadhuis or Town Hall. See Pl. VI, opp. p. 32. 

* “This House hates, loves, punishes, keeps, honours; Wickedness, 

Peace, Crimes, Oaths, the Righteous.’ This inscription is no longer to be 
seen—having been removed in the process of subsequent ‘‘ restoration.” 

* The New Church. 
* William I, the Silent (1533-1584); Stadholder. 
* William III of England and Orange (1650-1702). 

* The Old Church, where L. himself now also lies. See Pl. XIV, opp. 
p. 100. 

" Admiral Maarten Tromp (1598-1653). 

* Admiral Piet Hein (1572-1629).—All the tombs and places mentioned 
by Mountague can still be seen. 


insipid, and indeed is but weak, compar’d to the English, 
having little or no relish of the Mault.’ 

Mountague forgot, however, to mention the trees and the 
waterways which are still so typical of the town; so I 
would complete his picture by adding a few touches from a 
modern historian” who wrote of a time still earlier than 
Leeuwenhoek’s : 

It was a quiet, cheerful, yet somewhat drowsy little 
city, that ancient burgh of Delft. The placid canals by 
which it was intersected in every direction were all 
planted with whispering umbrageous rows of limes and 
poplars, and along these watery highways the traffic of 
the place glided so noiselessly that the town seemed the 
abode of silence and tranquillity. These streets were 
clean and airy, the houses well built, the whole aspect 
of the place thriving 

And writing of the same period, the Earl of Leicester— 
Queen EHlizabeth’s favourite, who was once, by a strange 
freak of fortune, Governor-General of the Netherlands—even 
describes Delft as “another London almost for beauty and 
fairness.” * 

But to return to our subject proper. On 29 July 1654* 

’ Delft was always famous for her beer: but the author of Batavia 
(1588) agreed with Mountague that it was inferior to the English— 
“ Cerealis potus prima post Britannicum zythum laude,’ etc. (p. 260). 
Dr Hadrianus Junius (alzas Adriaen de Jongh) doubtless knew what he was 
talking about, for he was at one time resident family physician to the Earl 
of Norfolk (ef. Bense, 1925, p. 198). 

* Motley, Dutch Republic: last chapter ad init. 

* Quoted by Motley, United Netherlands (1869), Vol. I, p. 352. The 
words are from a letter written by Robert Dudley, Earl of Leicester (1532 ?- 
1588), to Lord Walsingham on 26 Dec. 1585. He adds (fide Motley) “ the 
other towns I have passed by are very goodly towns, but this is the fairest 
of them all.” 

“ Haaxman (1875, p.16) gives the date as 26 July 1654. Bouricius 
(1924) says 29 June 1654: but in a letter he informs me that this is a 
misprint, and that the date given above is correct. According to Mr 
Bouricius the archives of Delft show that the marriage was formally 
announced on 11 July 1654, and registered on the 29th of the same month. 
Schierbeek (1930) correctly gives the date as “ 11/29 Juli 1654’"’"—July 11 
being the date of the ondertroww (corresponding roughly with “calling the 


when he was not quite 22 years old, Leeuwenhoek married 
Barbara, the daughter of Elias de Mey’ and Maria Virlin?— 
a@ young woman three years his senior.» The marriage took 
place at the New Church in Delft. From this union five 
children were born—three sons and two daughters—all but one 
of whom died in early infancy.*’ The one who survived was 
Maria, the second child, born on 22 September 1656. She 
lived to a great age, but never married. She stayed with her 
father Antony all his life, and ultimately buried him in the 
Old Church of Delft—in a tomb wherein she was herself 
interred in 1745, aged close upon 89 years’. Maria van 
Leeuwenhoek was no “‘ scientist,’”’ but she was a good daughter : 
we shall meet her again later. She kept house when her 
father was at work, she kept himself when he was weak, and 
she housed his body when he was dead. She will not be 
forgotten while her father is remembered. 

The year of Leeuwenhoek’s marriage (1654) was long 
recollected in Delft: for this was the year of the terrible 
explosion of the powder-magazine—a disaster which wrecked 
the whole town, and killed untold hundreds of the inhabitants’. 
The Queen of Bohemia’, writing to Sir Edward Nicholas* from 
The Hague a week later (19 October 1654), says :° 

banns” in an English church), and July 29 that of the actual marriage 
ceremony (huwelijk). 

* It may be of interest to English readers to note that Elias was at one 
time a cloth-merchant in Norwich (fide Bouricius). 

* Maria’s surname is given as “ Viruly”” by Haaxman, but Mr Bouricius 
assures me that this is incorrect. She came from Utrecht—not Delft. 

* Barbara de Mey was born 20 Dec. 1629 (fide Haaxman and Bouricius ; 
and cf. Schierbeek, 1930). 

“The three sons—all named Philips—were born in 1655, 1663, and 
1664. The daughter who died (1658) shortly after birth was named 
Margriete. See the Family Tree, p. 18. 

* Maria died on 25 April 1745. The dates of her birth and death, as 
here given, are those graven on the tomb. 

° Cf. Boitet (1729), p. 564 octies. The explosion involved some 80 or 90 
thousand pounds of gunpowder and happened at 11.30 a.m. on Monday 12 
Oct. 1654. The event is not mentioned—so far as I know—by L. Among 
those who perished was Karel Fabritius, the famous painter—supposed by 
some (on very slender evidence) to have been Vermeer’s master. 

" Elizabeth Stuart (1596-1662), sister to Charles I of England. 

* Edward Nicholas (1593-1669), Secretary of State to Charles I and 
Charles II. 

* Published in Bray’s edition (1827) of Evelyn’s Memoirs, Vol. V, p. 204. 


I was at Delft to see the wrack that was made by the 
blowing up of the powder this day seuenight, it is a sad 
sight, whole streets quite razed; not one stone vpon 
another, ib is not yett knowen how manie persons are 
lost, there is scarse anie house in the toune but the tyles 
are off. 

A happier event which occurred in the same year, however, 
was the conclusion of peace—for a time—between Holland and 

At about this date Leeuwenhoek bought a house and shop 
in Delft, and set up in business as a draper. For these 
premises he paid altogether—including interest on the money, 
which he had to borrow—5000 florins’. His house was 
situated’ in a street still called the Hippolytusbuurt, running 
parallel to the Oude Delft (the main canal and thoroughfare of 
the town), and within sight of the Old Church and the New 
Church’, and near to the Fish and Meat Markets and the 
Town Hall—all which places are mentioned by Leeuwenhoek 
and can still be seen by the inquiring traveller. But 
Leeuwenhoek’s house itself is no longer there. According to 
Bouricius, to whom the identification of the site is due, it 
was the second one from the Nieuwstraat (which connects 
Hippolytusbuurt with Oude Delft) and was called ‘‘ The Golden 
Head” (Het Gouden Hoofd). A few further details regarding 
it can be gathered from certain passages in the Letters. 
Leeuwenhoek lived in this house for the rest of his life, and 
there can be little doubt that it was here he made most of his 

By great good fortune, two of the bills which Leeuwenhoek 
made out for his customers have recently been recovered. 
They prove conclusively that he carried on business as a 

" Cf. Schierbeek (1929a). The facts were ascertained by the late Mr 

* This was forgotten until quite recently, when it was rediscovered by 
Morre (1919) and Bouricius (1924). Of. p. 338 infra. 

* These Churches are still called “Old” and “ New,” as they were in 
L.’s day. The “New” one, however, is not very new, as it was built 
between 1391 and 1496; while the “ Old”’ Church was probably built about 
1240. Cf. Boitet (1729) and Wildeman (1903). 

* Cf. p. 338 infra. 


draper and haberdasher, and are the earliest known examples 
of his handwriting. The shorter of these bills is here 
reproduced’ in Plate V: the longer and earlier shows similar 
items (silk, cloth, buttons, tape, ribbon, braid, etc.) sold to 
Johannis Heijnsbroeck in 1658. In view of its singular 
interest I give a complete translation of the bill exhibited 
in the Plate: 

Praise be to God! the 19th day of December 1659. In Delft. 
Mr. Pieter Heijnsbroeck debtor 

To Antony Leeuwenhoeck for the following 
— Shop-wares — 

4t ells* red kersey - - - @ 26 stivers th’ell - - - | 5.| 10.{ 8.° 
24 dozen buttons and button-loops - - - - - - - - pata i eel hese 
1 ell white bombazine @ 9 stivers - - - - -- - - Ae a es 
ogra cilicc= Case Stia ats cane eae too eee ou xia Gees 
24th ditto | 2 ells wide filoselle [?] ribbon - - - - - - - - - - - =| (ta eos 

Total, G2) L723: 

The contents hereof paid unto me 
this 15th day of June in the year 1660. 
Antony Leeuwenhoeck 

Leeuwenhoek’s wife Barbara died on 11 July 1666,* when 
they had been married twelve years: and not long afterwards 
—on 25 January 1671°—he contracted a second marriage with 

*This little document has already been printed by Morre (1919), who 
discovered it among the estate-papers relating to the Delft “court of 
chancery ” (Boedelpapieren der Delftsch Weeskamer, dossier No. 105). It 
has also been referred to by Mr Bouricius, to whose widow and Dr A. 
Schierbeek I am indebted for the photograph from which my plate has been 

*The Dutch ell at this period was approximately a modern metre, and 
therefore less than an English ell (45 inches). 

*The columns stand respectively for florins (guilders), stwivers (stivers), 
and pennings. 16 pennings—1 stuiver; and 20 stuivers = 1 florin (about 
1/8 in modern English money). 

* fide Haaxman. She was buried on July 14 in the Old Church 
(Schierbeek, 1930). 

° fide Bouricius. 


= a ae , O° ~. ” N¢, ™ s° Py (5 Qn dae 
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Laus Deo adij 19°". Xmb. a°: 1659. In Delff 
8S". Pieter Heijnsbroeck Debitt 
Aen Antonj Leeuwenhoeck over volgende 

47 el Root carsaij - - &’el F5:10:8 
2% dosijn Knoopen en Knooplussen - F'-: 6: - 
fel Wit Bombasiin: 4.9 st.- = =< - |) 4A ee soee 
Aen Roo Si. - =. = See Wea ls fou (aires 
247; ditto. 2. el breet Wijasel Lint - - - - = #-: 6: 
Sa eG he cS 

Den Inhout deses mij voldaen 
Adij 15. Junij a°: 1660 
Antonj Leeuwenhoeck 

facing p. 80 


a kinswoman of hers named Cornelia Swalmius.’ It is said 
that she bore him another child, who died in infancy :? and. 
Bouricius states that Cornelia herself died in 1694.° 

It is probable that Leeuwenhoek carried on his drapery 
business for many years—from the time of his first marriage 
(1654) onwards. We have no direct information about him 
again, however, until six years later, when he was made 
Chamberlain to the Sheriffs of Delft. He held this post for 
39 years; and thereafter, till his death, continued to draw 
the salary attaching to it. At the date of his nomination 
Leeuwenhoek was only 27 years old: for according to an 
entry in the town archives he was appointed—retrospectively, 
as it appears—on 26 March 1660, in succession to one Jan 
Strick (otherwise unknown). The full title of this office’ was 
“Chamberlain of the Council-Chamber of the Worshipful 
Sheriffs of Delft,’ and the terms of appointment were as 
follows: ° 

‘alias Kornelia Zwalmius (sew van der Swalm). The name is spelled 
variously. According to van Bakkenes (1873) and van der Baan (1874) she 
was the daughter of Johannes Swalmius (1621-1661), a clergyman of Valken- 
burg. The date of her birth is apparently unknown, but she must have 
been much younger than L., as her father was only 11 years his senior. 

* Boitet (1729), Haaxman (1871, 1875), and Bouricius (1924). It is said 
by van Bakkenes (1873), however, that L.’s second marriage was childless. 
In any case, no child of this marriage survived. 

* Buried 6 Jan. 1694; fide Schierbeek (1930). That she was alive in 1677 
can be inferred from a passage in a letter written in this year (Letter 22, 
Nov. 1677. Phil. Trans. (1678), Vol. XII, No. 142, p. 1040): and that she 
was dead in 1700 is directly attested by L. himself, who then refers to her 
as ‘my late wife”’ (Letter 130, 27 June 1700). 

“ Curiously enough, L.’s civil appointments are not mentioned in Boitet 
(1729); and it is perhaps for this reason that Banga (1868, p. 610) refers 
to him—incorrectly—as “a simple citizen of Delft, holding no office.”” L.’s 
appointment as Chamberlain was first reported by van Haastert (1823), who 
quotes no authority for his statement. 

>“ Camerbewaarder der Camer van Heeren Schepenen van Delfi.” The 

Schepens, or Sheriffs, were important civil dignitaries at this period. But 
Schout and Schepen have no exact English equivalents, so I can translate 
such words only approximately. 

° This entry was extracted from the town records by Mr J. Soutendam, 
sometime Town Clerk and Archivist (Archivaris en Secretaris) of Delft. It 
has already been published in full by Haaxman (1871, p. 14 sq.; 1875, p. 20 
sq.) and by Soutendam (1875), from whose printed Dutch transcriptions 
I translate. The information on this subject which Richardson (1885), 



Their Worships the Burgomasters and Magistrates of 
the Town of Delft have appointed and do hereby charge 
Antony Leewwenhoek to look after the Chamber wherein 
the Chief Judge the Sheriffs and the Law Officers of this 
Town do assemble: to open and to shut the foresaid 
Chamber at both ordinary and extraordinary assemblies 
of the foresaid Gentlemen in such wise as shall be required 
and needful: ztem to show towards these Gentlemen all 
respect honour and reverence and diligently to perform 
and faithfully to execute all charges which may be laid 
upon him and to keep to himself whatever he may over 
hear in the Chamber: to clean the foresaid Chamber 
properly and to keep it neat and tidy: to lay the fire at 
such times as it may be required and at his own con- 
venience and carefully to preserve for his own profit 
what coals may remain unconsumed and see to it that 
no mischance befall thereby nor from the hght of the 
candles: and he shall furthermore do all that is required 
of and that pertaineth to a good and trusty Chamberlain. 
For the which service the foresaid Antony Leeuwenhoek 
shall enjoy such wages benefits and emoluments as the 
foresaid lamented Jan Strick his predecessor in office did 
enjoy and shall enter into his duties upon the morning 
of the 24th of January 1660 and his wages shall be paid 
upon the same terms as those whereon the foresaid Jan 
Strick’s were paid. Ordered by all the Burgomasters in 
Council assembled this 26th day of March 1660 and 
signed by 

J. Camerling, Pensionary. 

Locy (1901, 1910, 1925), and Plimmer (1913) give, and which is stated by 
them to have been derived from the researches of Dr A. Wynter Blyth 
[a writer on toxicology and food-analysis, and Medical Officer of Health for 
St. Marylebone, London], is evidently nothing but a garbled version of 
Haaxman. There is no evidence to support Locy’s statements (1910, p. 78; 
1925, p. 207) that Wynter Blyth himself examined the town archives— 
which seems to be merely a mistaken inference from Richardson’s loose 

facing p. 32 




[ine os antiert | 






The Sheriffs’ 

d from the Market Place. 


Eastern (front) aspect, 

Chamber was in the second storey, on the north side (right in picture). 

From an old engraving. 

oe a 

se hn 
nae i 
PAS oy 
id ie 


From the treasurer’s accounts it appears that the emolu- 
ments attaching to this appointment amounted, in all, to 314 
florins per annum.’ Later entries show, however, that by 
1699 Leeuwenhoek’s grant had been increased to 400 florins 
yearly ; while a still later entry,” in 1711, shows that at that 
time he was receiving an additional salary of 50 florins for 
his services as “ generaal-wykmeester’’—an office resembling 
that of an English alderman. Both these municipal appoint- 
ments were probably sinecures, and their menial obligations 
performed by proxy. I note this in order not to convey the 
impression that Leeuwenhoek was really—as Richardson and 
Plimmer would have us believe—a sort of village beadle.* It 
is hardly necessary to add that 450 florins represented a much 
larger sum of money in the XVII Century than they do 

To preserve the historic perspective I must here venture 
once more to remind the reader of contemporary affairs in the 
world at large. In 1664, when Leeuwenhoek was 32 and had 
been Chamberlain for some 4 years, his mother—as we have 
already heard—died: but in this same year another memorable 
event also occurred. England and Holland were then again 
at war; and our Admiral Holmes* attacked and captured the 
Dutch colony of New Amsterdam on Manhattan Island in 
North America, and changed its name to New York in honour 
of his chief—the Duke of York, afterwards our King James II. 
Englishmen, Hollanders, and Americans—not to mention 
men of other nations—therefore have good reason to 
remember this epoch. But we must return to our real hero, 
who wisely took not the least notice of politics or warfare. 

It has recently come to light that Leeuwenhoek was not 
only a draper and sheriffs’ chamberlain but also a qualified 

‘The sum was made up as follows: For acting as Chamberlain, 
260 florins; for cleaning the Chambers of the Sheriffs, Council, etc., and 
on account of expenses necessarily incurred thereby, 54 florins. (Haaxman, 

* Quoted by Haaxman (1875). 

* Bedellus immortalis Richardson (1885)—unblushingly borrowed by 
Plimmer (1913)—is not only an unsuitable designation for L. but is in 
addition (under the Rules of Nomenclature) an invalid synonym of the more 
adequate name Homo sapiens Linnaeus. 

“Sir Robert Holmes (1622-1692), a great but now almost forgotten 
warrior who distinguished himself on many other occasions. 



surveyor. This discovery illuminates various passages in 
his letters, where he enters into arithmetical calculations 
regarding areas, volumes, heights, magnitudes of organisms, 
and so forth. ‘The act of his admission as_ surveyor 
(landmeter) in 1669 is extant in the Dutch State Archives, 
and seems sufficiently interesting to quote. It runs as 
follows :” 

denizen of the town of Delft, hath made petition unto the 
Court of Holland, saying that he hath for some while 
heretofore exercised himself in the art of Geometry, and 
advanced so far that he deems himself capable to fulfil 
henceforth the office of surveyor, and perform the service 
and duty thereof, wherefore he humbly intreateth that 
the Court be pleased to permit him to exercise the office 
of surveyor, after previous examination and trial of his 
ability : ACCORDINGLY, the said Court, having heard the 
report of the commissioner appointed thereunto, in whose 
presence the applicant was examined by the mathematician 
Genesius Baen* as to his aptness for the performing the 
foresaid office of surveyor, wherein he was found competent, 
hath allowed the application and hereby authorizes the 
applicant to perform the office and duty thereof, within 
the jurisdiction of the Court ; and hath administered unto 
him the statutory oath, that he acquit himself well and 
truly therein, by the hands of Mr. Pieter Ockers,’ councillor 

ee ——— 

‘ Ascertained by the late Mr Bouricius, though not published by him. 
It appears that Dr Baart de la Faille, archivist of Haarlem, supplied him 
with the reference to the relevant entry in the Archives. Cf. Schierbeek 
(1929a, 19380). 

2 Extract from 12de memoriaalboek van mr. Adriaens Pots, fol. 17. 
Rijksarchief : fide Schierbeek (1929a, 1930). Dr Schierbeek first published 
the entry from Mr Bouricius’s MS. remains; and the above is my English 
translation of his printed versions, checked by a photographic copy of the 
Dutch original which he has kindly sent me. 

* The name is so spelled in the original. 

4 Paen Schierbeek (1930) : a misreading. 

5 Ochers according to Schierbeek (1930); but this is also an obvious 
misreading or misprint. 




anDYET au. 

‘(GLOIT-GE9T) teomtoA uve Aq Suyured-io ayy 





gy Woy 


facing p. 35 


at Court, and commissioner appointed therefor. Ordered 

in Council the 4th day of February 1669. 

There is at least one direct reference to surveying in 
Leeuwenhoek’s writings, and it now acquires new significance 
in the light of the foregoing record. In the postscript to a 
letter written in 1713—containing some celebrated remarks 
on whales—he wrote: ' 

The height of the Tower of our New Church” was 
measured many years ago by me and the late Surveyor 
Spoors, each with his own quadrant, and found to be 299 
feet high 

For the year 1676 there is an entry in the Archives of Delft 
which illuminates Leeuwenhoek from an entirely different 
angle. Under date 30 September it is there recorded : ° 

Their Worships the Sheriffs of the Town of Delft do 
hereby appoint Anthonij Leeuwenhouck* to be Trustee ” 
for the estate and property of Catharina Bolnes, widow 
of the late Johannes Vermeer (in his lifetime Master 
Painter) and petitioner for a writ of insolvency,” for what 
he remained possessed of . . . Ordered the 30th of 
September 1676. 

Now the incomparable artist Jan Vermeer was born at 
Delft in the same year as Leeuwenhoek himself (1632), their 

' Send-brief IV, 14 March 1713. To Jan Meerman, Burgomaster of 
Delft. Published (Dutch) in Brieven, Vol. IV, p. 38; (Latin) Op. Omn. 
Vol. IV, p. 38. (No MS. and not in Phil. Trans.) 

* Visible in Vermeer’s view (Plate VII)—in the distance, to the right of 
the middle line. 

® Kamerboek der Stad Delft, 1671-1684: fide Obreen (1881-2), who has 
published the entry (p. 295) and from whose printed Dutch version I translate. 

* So spelled in original, fide Obreen. 

> Curateur orig. 

° Impetrante van mandement van cessie orig. These legal terms have no 
exact equivalents in modern English, though their meaning seems plain. 
According to Meijer’s Woordenschat (1745), impetrante = verkrijgster and 
mandement = bevel: while ‘‘mandement van cessie’’ is there explained as 
‘om zyne inschulders te mogen dagen’’, and “ Brieven van cessie’’ are defined 
as ‘ Brieven van Boedel afstand te mogen doen.” 


baptisms’ being entered on the very same page of the Register 
of the New Church: and he married Catharina Bolnes (alias 
Bolenes) on 5/20 April 1653. He was buried in his native 
town on 15 December 1675 at the early age of 43, leaving his 
widow with eight children (all under age), an insolvent estate, 
and some of the world’s finest pictures. ‘To meet her creditors 
Catharina Vermeer was forced to file a petition in bankruptcy 
and realize her assets: whereupon—as we see—the Sheriffs 
nominated Leeuwenhoek to act as “curator” or “ official 
receiver”. Everything regarding this affair now ascertainable 
from the Delft Archives has already been extracted and 
published by Obreen (1881-2) and Bredius (1885) ; and as the 
incident has but little present interest, | must refer readers 
seeking further information to their publications.’ 

Obreen has inferred* that Leeuwenhoek’s appointment as 
administrator of Vermeer’s estate was one of the “ pickings ” 
to which he was entitled by virtue of his office as Chamber- 
lain. Obreen may be right: but it seems hardly likely that 
Leeuwenhoek derived any profit from his trusteeship of the 
affairs of an insolvent family, and the extant records (as 
published) show only that he met with worries and legal 
difficulties in the discharge of his duty. To me the incident 
appears rather to indicate that Leeuwenhoek may have been a 
personal friend of the Vermeers, though it also shows clearly 
that he himself must have held a solid position as a citizen of 
Delft at that date; since it is inconceivable that the Sheriffs 
could have nominated anybody but a respected fellow- 
townsman to disentangle Vermeer’s involved finances. 
For Vermeer—though soon forgotten and only recently 
rediscovered—was then rightly regarded as a great artist and 
ornament of the Town, and his wife apparently had well-to-do 

' Vermeer’s was registered on 31 Oct. 1632: so this was not the date 
of his birth—as many writers state. The date of his birth is actually 

* I have had considerable difficulty in ascertaining the above particulars 
about Vermeer and his relations to Leeuwenhoek, because most biographers 
of both these great Delvenaars give little or no trustworthy information on 
the subject. On Vermeer cf. also Plietzsch (1911), Vanzype (1921), Lucas 
(1922), Chantavoine (1926). 

* Obreen (1881-2), p. 295. 


One other municipal function which Leeuwenhoek is now 
known to have discharged is that of wine-gauger (wijnroeijer)." 
He was elected to this post on 15 August 1679, and apparently 
occupied it (partly by proxy) for the rest of his life. The 
terms of this office are too long to print here in extenso. It 
must suffice to note that the wine-gauger had to assay all 
wines and spirits entering the town, and to calibrate the 
vessels in which they were contained; while he was himself 
debarred from engaging in any trade connected with liquor.” 
This appointment again throws some light upon our Leeuwen- 
hoek: for his personal knowledge of wines—including their 
effects and antidotes—will be evident to all attentive readers 
of his letters. 

From the date of his appointment as Chamberlain in 1660 
nothing was heard of Leeuwenhoek outside of Delft for thirteen 
years, though we may be sure that he was not idle during this 
interval. But in 1673 we hear of him again in an altogether 
unexpected connexion. Our Dutch Draper-Chamberlain is 
now suddenly discovered to us as an amateur of science— 
offering a paper, containing some modest original observations, 
for publication in the Philosophical Transactions of the Royal 
Society of London. 

How this came about is soon told. The Royal Society, 
then but recently founded,* was eager to get into communica- 
tion with allmen—no matter what their rank or nationality— 
who were working for “ the promotion of natural knowledge” : * 
and in this endeavour it was successful, in no small measure, 
through the efforts of its energetic secretary Mr Oldenburg 

1 First recorded by Morre (1919) and Bouricius (1925). The latter has 
kindly supplied me (from the archives of Delft) with full particulars—partly 
given above—relating to the functions of a wine-gauger.—There is, I find, 
an early Dutch work on gauging by Cornelis van Leeuwen (1663), with 
which L. was probably familiar and which describes the technique fully. 

? Since these lines were written Schierbeek (1929) has published the 
regulations regarding the office of wine-gauger in greater detail. 

° Readers desirous of knowing more about this historic event may be 
referred specially to the works of Sprat (1667) and Weld (1848); and also 
to the more recent Record of the Roy. Soc. (1912) and the posthumous 
publication of Miss Ornstein (1928). 

*“They [the Royal Society] exact no extraordinary praeparations of 

Learning: to have found Senses and Truth, is with them a sufficient 
Qualification” (Sprat, 2 ed. (1702), p. 435). 


(Plate VIII). His foreign correspondence was enormous, as 
can be gathered from the manuscript letters to and from him 
still preserved by the Society. Among the Roy. Soc. MSS. 
(to mention no others) are drafts of more than 400 letters— 
apart from numerous translations and many other documents— 
written by Oldenburg to various more or less celebrated and 
scientific persons between the years 1657 and 1677: while the 
extant letters addressed to him well exceed 1200 in number. 
Henry Oldenburg (1615 ?—1677),* first Secretary of the 
Royal Society,” was a remarkable man. He was a German 
of good family—a native of Bremen—who came to England 
about 1640 and afterwards played a prominent part in con- 
temporary English scientific life. He is now chiefly remem- 
bered, however, as a translator and as the first editor of the 
Philosophical Transactions and as a correspondent with nearly 
all outstanding “ philosophers” and “virtuosi” of his day. 
Curiously enough, no adequate biography of this influential 
figure in the History of Science has ever yet been published. 
It may be noted in passing that several scientific letters 
written to Oldenburg—including some of Leeuwenhoek’s— 
are addressed to ‘“‘ Mr. Grubendol”’. He sometimes used this 
anagram when corresponding with foreigners, apparently, in 
order to avoid suspicion through receiving too many com- 
munications from abroad in his proper name. It was a 
transparent subterfuge which reflects no discredit upon him: 
but that his fears were well founded is clear from the fact 
that he was actually imprisoned, as a suspected spy, towards 
the end of June, 1667. Pepys,’ in his Diary, under the 
date 25 June 1667, notes: “I was told, yesterday, that Mr. 
Oldenburg, our Secretary at Gresham College, is put into the 

‘For his life see Birch, Vol. III, p.3853; Rix (1893); and the Dict. 
Nat. Biogr. The date of his birth is not certainly known; but it was not 
1626, as usually stated. 

> Jointly with John Wilkins (1614-1672), D.D.; Master of Trinity 
College, Cambridge (1659); later Bishop of Chester (1668). Wilkins was 
also a man of considerable parts. A collective edition of his ‘mathematical 
and philosophical works”’ appeared in 1708 (with a portrait and the author’s 
life prefix’d). 

* Samuel Pepys (1633-1703) was elected Fellow of the Royal Society in 
1665 and President in 1684. 


Fioyal Society London 
HENRY OLDENBURG (1615 ?-1677) 

First Secretary of the Royal Society, 1663-1677 

From an oil-painting by Jan van Cleef (1646-1716) made in the year 1668. 

facing p. 38 

ee we Kaw, | hs : 

es nr) en re) 

nN af Y , uy 
| Y ee ieee a) 


Tower, for writing newes’ to a virtuoso in France, with 
whom he constantly corresponds in philosophical matters; 
which makes it very unsafe at this time to write, or almost 
do anything.” Weld,’ who has given a more circumstantial 
account of this incident, calls it “a very remarkable event 
which seems to have had so much influence upon the Society 
as to cause a suspension of the Meetings from the 30th May 
to the 3rd October”. Yet the event appears less remarkable 
when we remember that the citizens of London—already 
severely shaken by the Great Plague and the Great Fire of 
the two previous years—were listening, for the first time, 
to the guns of a foreign fleet advancing up the Thames 
at the moment when they clapped Oldenburg in jail. Evelyn 
says*® “‘The alarme was so greate that it put both Country 
and Citty into a paniq, feare and consternation, such as I 
hope I shall never see more.”” But the Londoners were then 
feeling far more afraid of the fierce Dutch Admiral de Ruyter 
than of the mild German-English scientist, and poor Olden- 
burg was soon exonerated. On his release from the Tower he 
wrote to Boyle (8 September 1667): “I hope I shall live fully 
to satisfy his majesty and all honest Englishmen of my 
integrity, and of my real zeal to spend the remainder of my 
hfe in doing faithful service to the nation to the very utmost 
of my abilities’: which he did. 

Among Oldenburg’s innumerable correspondents was the 
youthful but already famous Dutch physician Reinier de 
Graaf,’ a friend and fellow-townsman of Leeuwenhoek. (See 

_ ‘Cf. also Evelyn (Diary, 8 Aug. 1677) : ‘‘ Visited Mr. Oldenburg, a close 
prisoner in the Tower, being suspected of writing intelligence.”’ 

* Weld (1848), I, 201 sq. 

* Diary, 18 June 1667. John Evelyn (1620-1706) was an original 
Fellow of the Royal Society, and Secretary in 1672. 

* Reinier [sew Regnerus ] de Graaf (1641-1673) was born at Schoonhoven, 
studied under Sylvius at Leyden, and practised (and died) at Delft. His 
anatomical researches——especially upon the organs of generation—are still 
well known. The “ Graafian follicle’? of the ovary (which he regarded as 
an egg) enshrines his memory. His Opera Omnia were first published 
posthumously at Leyden in 1677. (L. has left it on record that his 
untimely death was hastened by his embittered controversy with 
Swammerdam over the priority of their anatomical discoveries.) He did 
not live to be elected a Fellow of the Royal Society, but died at the age of 
32, after a brief but brilliant career, in the very year in which he introduced L. 


Plate [X.) During the silent ,eriod preceding the year 1673 
Leeuwenhoek was evidently engaged—in his spare time, when 
he was not selling buttons and ribbon—in making lenses, and 
mounting them to form “ microscopes ”’ of simple pattern: and 
after he had acquired much skill in the manufacture of these 
curious instruments,’ and had taught himself how to grind and 
polish and mount lenses of considerable magnifying power, he 
began to examine all manner of things with their aid. Dr 
de Graaf was personally acquainted with Leeuwenhoek’s work, 
and had had. opportunities of inspecting various objects 
through his glasses. 

In the Philosophical Transactions for 1668 the editor had 
published’ an extract from the Giornale dev Letterati, con- 
taining an account of a new microscope made by Hustachio 
Divini in Italy. With this instrument, it was claimed, he 
had been able to discover “an animal lesser than any of those 
seen hitherto.” It was doubtless as a counterblast to this 
sweeping assertion, and with pardonable patriotism, that 
de Graaf (28 April 1673) addressed himself to Oldenburg in 
the following words :* 

That it may be the more evident to you that the 
humanities and science* are not yet banished from among 
us by the clash of arms,’ I am writing to tell you that a 

* Cf. p. 313 sq., infra. 

* Phil. Trans. (1668), Vol. III, No. 42, p.842—then edited by Oldenburg. 
Divini’s portrait can be seen in the work of Manzini (1660). 

* The original letter, from which I here translate a part, is still preserved 
by the Royal Society (MS. No. 1168; G.Z. 11). It is written in Latin, and 
an extract—in English—was published in Phil. Trans. (1673), Vol. VIII, 
No. 94, p. 6037. The letter was read at the meeting of the Society held on 
7 May 1673 [0.S.], when L.’s first observations were also communicated. 
Cf. Birch, Vol. III, p. 88. 

* studia humaniora et philosophica MS. 

° I may remind the reader that a European war was being waged at this 
time, and that England was actually at war with Holland. Peace was not 
concluded between us until February, 1674; but communications apparently 
remained unbroken throughout—probably because “the Nations had been 
at War without being angry; and the Quarrel had been thought on both 
Sides rather of the Ministries than the People’”’ (Sir William Temple (1709), 
Memoirs [1672-1679] p.3). Contemporary writers, both in England and 
in Holland, afford numerous other gratifying instances of the lack of personal 
enmity between our two peoples. For example, the Earl of Castlemain 


LNs itt 




if Hi 



it i | 

REINIER DE GRAAF (1641-1673) 



From the unsigned engraving prefixed to his posthumous Opera Omnia. 

fucing p. 40 


certain most ingenious person here, named Leewenhoeck,' 
has devised microscopes which far surpass those which 
we have hitherto seen, manufactured by Eustachio Divini 
and others. The enclosed letter from him, wherein he 
describes certain things which he has observed more 
accurately than previous authors, will afford you a sample 
of his work: and if it please you, and you would test the 
skill of this most diligent man and give him encourage- 
ment, then pray send him a letter containing your 
suggestions, and proposing to him more difficult problems 
of the same kind. 

The enclosed specimen of Leeuwenhoek’s work consisted 
of various rather crude observations on Mould; on the sting 
and mouth-parts and eye of the Bee; and on the Louse. It 
was published in English in the Philosophical Transactions * 
with some comments by Oldenburg, who wound up by 
remarking (somewhat sardonically, I fear) “So far this 
observer: who doubtless will proceed in making and imparting 
more Observations, the better to evince the goodness of these 
his Glasses’”—a prophecy which was actually fulfilled more 
amply during the next fifty years than anybody could then 
have thought possible. Yet the Fellows evidently liked the 
observations, and Oldenburg was instructed to communicate 
with their author. To his letter Leeuwenhoek sent the 
following characteristic answer from “‘ Delff in Hollant”:* 

(1671, p. 97) remarks “We have now finisht a sharp and bloody War, which 
nevertheless leaves not the least rancor (that I know) in the heart of any 
English man; and the reason of it is, because we have generally an affection 
for these our neighbors [the Dutch], esteeming them an industrious and 
sober people’’. 

* So spelled in original. 

2 Letter 1. See Phil. Trans. (1673), Vol. VIII, No. 94, p. 6037. The 
original MS. has not been preserved by the Society, and is presumably no 
longer extant. 

® Translated from Letter 2 (15 August 1673). MS.Roy.Soc. The original 
is in Dutch. Cf. Plate X. The drawings were engraved and published in 
Phil. Trans. (1673), Vol. VIII, No. 97, but their originals are lost. The 
part of this letter here translated has not been published previously, but 
some extracts from the remainder were printed—in English, in two parts— 
in Phil. Trans. (1674), Vol. IX, No. 102, pp. 21-25. 



I have oft-times been besought, by divers gentlemen, to 
set down on paper what I have beheld through my newly 
invented Microscopia: but I have generally declined; 
first, because I have no style, or pen, wherewith to express 
my thoughts properly; secondly, because I have not been 
brought up to languages or arts, but only to business; and 
in the third place, because I do not gladly suffer contra- 
diction or censure from others. This resolve of mine, 
however, I have now set aside, at the intreaty of Dr Reg. 
de Graaf; and I gave him a memoir on what I have 
noticed about mould, the sting and sundry little limbs of 
the bee, and also about the sting of the louse. This 
memoir he (Mr de Graaf) conveyed to you; whereupon 
you sent me back an answer, from which I see that my 
observations did not displease the Royal Society, and that 
the Fellows desired to see figures of the sting and the 
little limbs of the bee, whereof I made mention. As I 
can’t draw, I have got them drawn for me, but the 
proportions have not come out as well as I had hoped to 
see ’em; and each figure that I send you herewith was 
seen and drawn through a different magnifying-glass. I 
beg you, therefore, and those Gentlemen to whose notice 
these may come, please to bear in mind that my observa- 
tions and thoughts are the outcome of my own unaided 
impulse and curiosity alone; for, besides myself, in our 
town there be no philosophers who practise this art; so 
pray take not amiss my poor pen, and the liberty I here 
take in setting down my random notions.’ 

Exactly a week before Leeuwenhoek dispatched the fore- 
going letter to the Royal Society, some further information 
about himself had been sent to one of the Fellows by 
Constantijn Huygens’—the once celebrated diplomatist and 

" gedachten, die ick als overhoop hier onderstel MS. It is difficult to 
render these words exactly in modern English. 

* Constantijn Huygens (1596—1687), statesman, poet, musician, and 
man of letters—‘ the most brilliant figure in Dutch literary history. Other 
statesmen surpassed him in political influence . . . but his talents 




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facing p. 42 


poet who is now best known to men of science as father of 
Christiaan Huygens the mathematician and astronomer. On8 
August 1673, Sir Constantijn wrote (in English, as here given) 
to Robert Hooke :* 

Our honest citizen, Mr. Leewenhoeck—or Leawenhook,* 
according to your orthographie—having desired me to 
peruse what he hath set down of his observations about 
the sting of a bee, at the requisition of Mr. Oldenburg, 
and by order, as I suppose, of your noble Royal Society, 
I could not forbear by this occasion to give you this 
character of the man, that he is a person unlearned both 
in sciences and languages, but of his own nature exceed- 
ingly curious and industrious, as you shall perceive not 
onely by what he giveth you about the bee, but also by 
his cleere observations about the wonderfull and trans- 
parent tuwbulc appearing in all kind of wood . . . His way 
for this is to make a very small incision in the edge of 
a box, and then tearing of it a little slice or film, as I 
think you call it, the thinner the better, and getting it 
upon the needle of his little microscope—a machinula of 
his owne contriving and workmanship—brass*®’ . . . I 
trust you will not be unpleased with the confirmations 
of so diligent a searcher as this man is, though allways 

were more varied, and his general accomplishments more remarkable than 
those of any other person of his age, the greatest age in the history of the 
Netherlands. Huygens is the grand seigneur of the republic’? (Edmund 
Gosse). He was also the friend and confidant of L. King James I knighted 
him in 1622—+ten years before L. was born. 

* The original letter is preserved among the MSS. in the Royal Academy 
at Amsterdam, and has been recently printed by J. A. Worp (1917), Brief- 
wisseling van Const. Huygens, Vol. V1; No. 6909, p.330. A part has been 
copied—not too accurately—by Vandevelde (1924a, p. 289), who wrongly 
dates the letter Aug. 3—On Hooke see note 1 on p. 47 infra. 

* Cf. p. 304 infra. 

* This word (brass, following a dash) occurs thus in the MS. but is 
omitted from the printed letter by the modern editor (Worp), who says it 
is “‘ unintelligible”. To me, however, it appears very easy to understand: 
Huygens meant that L.’s little microscope was “made of brass’’—as so 
many of his instruments were. 


modestly submitting his experiences and conceits about 
them to the censure and correction of the learned. 

The foregoing extracts show clearly how Leeuwenhoek’s 
relations with the Royal Society originated: and they dis- 
prove, I think, a statement which has been made elsewhere ' 
that he owed his introduction to Sir Constantijn Huygens. 

From the time when his words quoted above were written 
until the day of his death, fifty years later, Leeuwenhoek 
continued to send letters to the Royal Society. They cover 
an immense field, and contain observations on matters z0o- 
logical, botanical, chemical, physical, physiological, medical, 
and miscellaneous (unclassifiable). They are mostly—but not 
entirely—concerned with observations and discoveries made 
with the microscope. But this is not the place to speak of 
their contents in detail: and I shall only add here that many 
of them—but not all—were published, more or less curtailed, 
in English (or occasionally in Latin) in the Philosophical 
Transactions from 1673 to 1723; and that many of them— 
but not all—were issued fully in Dutch and Latin,’ as separate 
publications, in his lifetime. He himself spoke and wrote and 
understood Dutch only,’ and versions of his views in any other 
tongue suffer from the inevitable defects of translation and 
interpretation. Consequently, one must be able to read old- 
fashioned Dutch to read Leeuwenhoek: and for my own part 

* In the @uvr. Compl. de Chr. Huygens, Vol. VII, p. 316 (footnote)— 
published in 1897—it is averred (I know not by whom) that MS. letters at 
Amsterdam, which passed between L. and Constantijn Huygens (pater), and 
between the latter and Robert Hooke and Oldenburg, show that L.’s first 
relations with the Royal Society were established through the intermediation 
of Const. Huygens: but the documentary and other evidence at my disposal 
seems to show incontrovertibly that the statements made above are correct. 

* Tt is not now known who translated L.’s letters into Latin for the 
editions of his works in that language. It is obvious—from the Latin 
styles, and the period of time covered—that the translations were made by 
more than one hand; but all my attempts to solve this problem have 
hitherto been fruitless. At one moment I thought I had discovered the 
name of one of his translators: for in an English MS. version (unpublished) 
of one of his later letters there is a reference to the translator as © Mynheer 
Aalder”’. But on consulting the original, I found that this was merely a 
misreading of the words “de Heer vertaalder’’ [= the translator] in the 
Dutch manuscript ! 

* See p. 305 sq., infra. 


I would say that it is well worth the trouble of learning this 
admirable language merely for the pleasure of reading this 
admirable man’s admirable letters. 

All Leeuwenhoek’s recorded observations were described 
in letters. He never wrote a book or a scientific paper—only 
letters, and still more letters, addressed to all manner of 
people. His letters were all written by himself in his own 
old-fashioned Dutch, though they were often translated by 
others into other languages, published in many different ways, 
and collected in various volumes at divers dates by different 
editors. All his own original writings are distinguished by 
a certain businesslike formality, but almost total lack of 
coherence. After presenting his compliments, he just wrote 
down what he wanted to say at the moment—recording now 
perhaps a few experiments, with his speculations about their 
significance, then adding a few personal remarks, and winding 
up with a mass of further observations and thoughts on some 
totally different topic. He wrote much as he must have 
spoken, so that his letters have an extraordinarily colloquial 
and familiar flavour which conveys—to me, at least—a strange 
sense of intimacy. He wrote as loosely and discursively as 
other people usually speak—just as though he were talking 
to a friend who obviously understood his common everyday 
speech: and he was always so intent on telling what he had 
seen or thought that he had no time to worry about grammar 
or the niceties of literary composition. Consequently, his 
writings are more like conversations than formal letters. He 
would certainly have agreed with his sweet English con- 
temporary, Dorothy Osborne,’ when she said: “ All letters, 
methinks, should be free and easy as one’s discourse; not 
studied as an oration, nor made up of hard words like a charm. 
Tis an admirable* thing to see how some people will labour 
to find out terms that will obscure a plain sense... .”’ And 
he would also have agreed with James Howell’ that “ we 

* Dorothy Osborne (1627-1695) ; afterwards wife of Sir William Temple, 
sometime English Ambassador to Holland. I quote from Letter 33 of 
Parry’s edition of her letters to Temple. The words quoted were written at 
some unknown date in 1653. 

* Meaning, of course, “ wonderful” or ‘‘ marvellous’”’—not ‘‘ admirable”’ 
(=to be admired or approved) in the modern sense. 
* James Howell (1594 ?-1666), celebrated author, linguist, and letter- 

writer. I quote from the 1705 edition of his Hpistolae, p.1 (letter dated 
25 July 1625). 


should write as we speak; and that’s a true familiar Letter 
which expresseth one’s Mind, as if he were discoursing with 
the Party to whom he writes in succinct and short Terms.” 
But whether serious scientific work should be published in so 
plain and unceremonious a fashion is, of course, debatable 

Yet there can be no doubts in the mind of anyone who 
seriously studies his writings that Leeuwenhoek—as he so 
often tells us—worked entirely by himself. He received no 
help from contemporary microscopists, and was wholly 
inspired by his own inborn genius. Indeed, he disliked and 
resented interference, and distrusted the knowledge—and 
sometimes the purpose—of people who went to see him or 
who offered him advice: and for this he evidently had good 
reasons. Writing to Oldenburg as early as 1675 he 
remarked : * 

Your Excellency recommends me to make use of the 
services of other people, who are in a position to form a 
proper judgement of such things. Sir, I must say that 
there be few persons in this Town from whom I can get 
any help; and among those who can come to visit me 
from abroad, I have just lately had one who was much 
rather inclined to deck himself out with my feathers, 
than to offer me a helping hand. 

It was not until 1680, after Oldenburg had died and when 
he himself was in his 48th year, that Leeuwenhoek was 
elected a Fellow of the Royal Society. As the date and other 
details are frequently given wrongly by biographers I must 
here briefly chronicle the relevant facts. For his election 

* Carbone (1930) has recently tried to show that L. was inspired by the 
Italian workers of his time. But Carbone’s only evidence for this is a 
letter (attributed by him to L.) which he has “discovered”? among the 
Magliabechi MSS. at Florence. It is certain, however, that this letter 
(dated 2 May 1692) was not written by Leeuwenhoek but by Leibniz. (It 
is in Latin, and unsigned: but it bears Leibniz’s seal, much internal 
evidence of his authorship, was written from Hanover, and had previously 
been published as an authentic Leibniz letter by Targioni-Tozzetti in 1746.) 

*From Letter 12. 14 August 1675. To Oldenburg. MS. Roy. Soc. 
Incompletely abstracted in English in Phil. Trans. (1675), Vol. X, No. 117, 
p. 380. Not published elsewhere. 


was, to him, an event of the first magnitude, and an unfailing 
source of encouragement for the rest of his life. 

From letters still extant it appears that Hooke! wrote to 
Leeuwenhoek early in 1680, and expressed surprise that his 
name was not upon the list of Fellows of the Society: and he 
also then offered, apparently, to propose him for election. To 
this letter Leeuwenhoek replied” that he had “never had a 
thought of pretending” to such a distinction, though he 
would “thankfully have acceded if Mr Oldenburg, in his 
lifetime,” had afforded any opening”: and he would regard 
election to the Fellowship, he says, as “‘the greatest honour 
in all the world”’. 

This letter was written on 13 February 1680 [N.S.] in reply 
to Hooke’s dated 23 January 1680 [O.S.]; but the election 
actually took place on 29 January|O.S.|—before Leeuwenhoek’s 
answer could have been received in England. Moreover, 
Hooke was not the proposer : for it is recorded by Birch ‘—and 
accurately, as reference to the minutes shows—that on 29 
January 1679/80 [O.S.] “Dr. Heusch,° Mr. Firmin® and 

* Dr Robert Hooke (1635-1703), an original Fellow of the Royal Society, 
was also an original and eccentric genius and inventor. His contributions 
to science are too well-known and numerous to mention; though his 
influence on his contemporaries, and the part he played in the early days of 
the Society, are only just beginning to receive their due recognition. 
Inadequate accounts of his life will be found in Waller (1705) and the Dict. 
Nat. Biogr.—also in some more recent publications. It is impossible and 
unnecessary to discuss this remarkable man and his work here. 

* Letter 29b. 18 February 1680 [N.S.] to R. Hooke. MS. Roy. Soc. 
Unpublished. This letter was translated by Francis Aston, and read at a 
meeting of the Society held on 12 Feb. 1680 [0.S.]. Cf. Birch, Vol. IV, 
pel. j 

* Oldenburg died, it will be recalled, in 1677. Hooke and Grew were 
appointed Secretaries in the same year, while Gale succeeded to this office 
in 1679. 

; Bireh, Vol. FV, p.'6. 

* Johann Christian Heusch, M.D., principal physician to the Elector 
Palatine but otherwise apparently undistinguished. He attended a meeting 
of the Society on 22 Jan. 1680, and subsequently signed his name in the 
register. Cf. Birch, Vol. IV, pp. 5, 7. 

* Thomas Firmin (1632-1697), citizen of London, remembered only as a 
philanthropist. Though a Fellow of the Society he was not a man of 
science. See Dict. Nat. Biogr. and life by Cornish (1780). 



Mr. Houghton’ were elected; as was also Mr. Leewenhoeck 
upon the motion of Dr. Croune,’ and Dr. Gale* was desired to 
draw up a diploma to be sent to him.” 

There is thus ample documentary evidence to prove that 
Leeuwenhoek was elected a Fellow of the Royal Society—a 
full Fellow, and not a Foreign Member,’—on 29 January 
1679/80 [0.8.]; that is, on 8 February 1680 according to 
present-day reckoning [N.S.].’ He was proposed by Croone— 
not by Hooke—and his election was unanimous.° 

At the gathering of the Society on 12 February [0.S.] 
1680, ‘‘ Dr. Gale was called upon for the diploma directed at 
the meeting of January 29 to be sent to Mr. Leewenhoeck ; 
and it was ordered, that the society’s seal should be affixed to 
it, and that a silver box should be provided for it.”" Later, at 
the same meeting, “Dr. Gale produced his draught of a 
diploma for Mr. Leewenhoeck”’*: and on February 19, “it was 
ordered, that the arms of the society be ingraved on the silver 
box.”® Finally, at a meeting of Council on February 23, 
it was directed “‘ That Mr. Hunt” prepare a silver box for the 
diploma to be sent to Mr. Leewenhoeck ;”’" and on the 28th 

* John Houghton (?—1705), now imperfectly known as a writer on 
husbandry (especially on potatoes) and trade. See Dict. Nat. Biogr. 

? William Croone [sew Croune] M.D. (1633-1684), educated at Emmanuel 
College, Cambridge, was an original Fellow of the Royal Society and a well- 
known physician in his day. The “Croonian Lectures”’ still serve to 
perpetuate his memory. See Birch, Vol. IV, p. 339 and Dict. Nat. Buogr. 
for further details of his life and legacies. 

* Thomas Gale, D.D. See p. 193, note 2, infra. 

* “ Foreign Members” were an invention of a much later date. Cf. 
Nuttall (1921) and Dobell (1923). 

° Boitet (1729, p. 766) wrongly gives the date as 26 February 1679, and 
has been copied by Soutendam (1875) and others. 

® So Hookeinformed him. See Letter 31a,13 May 1680. To R. Hooke. 
MS. Roy. Soc. Unpublished. Cf. also p. 87 znfra. 

" Birch, Vol. IV, p. 11. 
* Birch, Vol. IV, p. 13. 
* Birch, Vol. IV, p. 13. 

* Henry Hunt was the Society’s ‘‘ operator,’ who assisted at demonstra- 
tions and in other ways. He filled the offices of laboratory attendant, 
assistant secretary, and general factotum—for £40 a year (when he could 
get it)—and left the Society a legacy on his death. 

” Birch, Vol. IV, p. 16. 


y '—_—_______. > -__ re - ‘ _ “i eicoses 
F = F 

fiijksmuseum Amsterdam 


From the oil-painting made in 1686 by Johannes Verkolje (1650-1693). 

facing p. 49 


“The president’ took with him the diploma for Mr. 
Leewenhoeck, and presented the Society with a screw-press for 
sealing such diploma’s.” ® 

Unfortunately the “‘ diploma,” though safely delivered * in 
Delft, is now lost; but it is portrayed in Verkolje’s oil-painting 
of Leeuwenhoek,* wherein it is shown as a vellum scroll with 
a pendent red seal. Curiously enough, it was apparently 
engrossed in Dutch’—not in Latin—in deference to the re- 
cipient’s ignorance. On receipt of this document, with its big 
red seal and in its engraved silver box, Leeuwenhoek returned 
the following acknowledgement :° 

Delft, 13th May 1680. 
To the President, Council, 
& Fellows of the Royal Society. 

I was quite taken aback to hear that the members of 
the Roy. Society had been pleased to confer upon me, all 
undeservedly, so much honour and dignity as to admit me 
a Fellow of the same most worthy College; as I first 
learnt from a letter written by Mr Secretary Thos. Gale, 
and a bit later through the receipt of a sealed Diploma ; 
whereof both were full of expressions on my behalf that 

Sir Joseph Williamson (1633-1701), statesman. 
> Birch, Vol. LV, p. 21. 

* Halbertsma (1843, p. 19) says he had heard [wt audivi’’—no 
authority quoted] that L. received the diploma from the British Ambassador 
at The Hague. This seems likely enough; but I have sought in vain for any 
confirmation of the statement. 

* Now in the Rijks-Museum (see Plate XI). It is not shown in Verkolje’s 
mezzotint (see Frontispiece). 

° Several words are clearly legible in the painting. 

° Letter 31b. 13 May 1680 [N.S.]. To the Royal Society. MS.Roy.Soc. 
Unpublished. The original is in Dutch, and the above is my translation : 
but I confess my inability to convey to the modern English reader the 
extraordinary mixture of formal and familiar, colloquial and commercial, 
and above all genuine and sincere phraseology of the ancient original. 
A similar letter (No. 31a, also unpublished) was sent to Robert Hooke 
personally at the same time (dated 13 May 1680 [N.S.] MS.Roy.Soc.). 
Both letters were communicated to the Society by Hooke on 13 May [0.8.]. 
Cf. Birch, Vol. IV, p. 37. 



my merits must fall far short of. Under which protest 
I notwithstanding hold myself most straitly pledged 
hereby, by unalterable intent and promise, to the Fellows 
of the said Society, for the signal favour they have shown 
me, to strive with all my might and main, all my life 
long, to make myself more worthy of this honour and 

Wherewith commending you, most noble Gentlemen, 
one and all, to the merciful protection of Almighty God, 

I remain, Gentlemen, 
Your most humble servant 
Antony Leeuwenhoek. 

An amusing sidelight is thrown upon Leeuwenhoek at this 
moment in his career by a passage in a letter to Christiaan 
Huygens from his brother Constantijn." Writing on 13 
August 1680 he says’: 

Everybody here is still rushing to visit Leeuwenhoek, as 
the great man of the century. A few months ago the 
people of the Royal Society in London received him 
among their number, which gave him some little pride ; 
and he even seriously inquired of Sir Father* if, being 
now invested with this dignity, he would be obliged in 
future to take a back seat in presence of a doctor of 
medicine ! 

Leeuwenhoek never came to London to sign the Register 
of Fellows or attend any meeting of the Royal Society. He 
was a busy man, and seldom went far from home—though he 
tells us of occasional short excursions from Delft in some of 
his letters. For example, in those here translated there are 

* Constantijn Huygens filius (1628-1697), son of Constantijn pater—the 
“grand seigneur”’ and English knight—and elder brother of Christiaan. 

2 Printed in Clwres Compl. de Chr. Huygens (1899); No. 2226, 
Vol. VIII, p. 295. The original MS. is in the University Library at Leyden, 
and is written in French—from which I translate. 

3 ql Signor Padre orig.—meaning Sir Constantijn, their father. 
Constantijn jun. sometimes lapsed thus into Italian when writing in French 
to his brother—whom he called occasionally “ fratello caro”’. 


references to holidays spent at the seaside (Scheveningen) and 
“in Brabant and elsewhere.” But he once, before his election, 
visited London—though this is not generally known—and 
recorded the circumstance in an unpublished passage in an 
early letter (1674). What he there says is so interesting, in 
more ways than one, that I must quote his words. In the 
course of describing some microscopic observations on the 
composition of chalk and clay, he unexpectedly adds’ : 

About six years ago, being in England, out of curiosity, 
and seeing the great chalk cliffs and chalky lands at 
Gravesend and Rochester, it oft-times set me a-thinking ; 
and at the same time I also tried to penetrate the parts 
of the chalk.” At last I observed that chalk consisteth of 
very small transparent particles*; and these transparent 
particles lying one upon another, is, methinks now, the 
reason why chalk is white. 

Tt is clear from his own words that Leeuwenhoek spent a 
holiday in England sometime during the year 1668." He came 
to London—sailing up the Thames by way of Harwich, 
Rochester, and Gravesend (after embarking probably at 
Rotterdam)—and brought a microscope with him. From this 
it seems legitimate to infer, therefore, that he was already 
engaged in his microscopic studies in 1668—at least five years 
before his first communication with the Royal Society. These 

1 Brom Letter 6,7 Sept. 1674. To Oldenburg. MS.Roy.Soc. Incom- 
pletely translated into English in Phil. Trans. (1674), Vol. IX, No. 108, 
pp. 178-182 [misprinted 821]. From this translation the passage here 
given was entirely omitted: and in the following paragraph (p. 181), where 
L. speaks of the colour of the English soil, “ die ick aldaer tusschen Harwits 
en Londen gesien heb”, his words have been altered to an impersonal 
statement about ‘‘ that, which 7s found between Harwich and London” [my 

2 de deelen van het krijt te penetreren MS. By this L. evidently means 
that he attempted to study the microscopic structure of chalk. No other 
interpretation—if the context be considered—appears to me possible. 

® clootgens MS. It is hardly possible to doubt that some, at least, of 
these “transparent particles” were fossil shells of Foraminifera. 

‘ England and Holland were then temporarily at peace. The second 
Anglo-Dutch War was concluded in July, 1667, and the third was not 
declared until March, 1672. 


observations on chalk are, so far as I have yet ascertained, the 
earliest dated microscopic investigations recorded by Leeuwen- 
hoek: and they dispose of a recent suggestion * that he began 
his career as a microscopist under the influence of his second 
wife—the “ blue-stocking’”’ Cornelia Zwalmius. He did not 
marry this supposedly learned lady ° until 1671; but the fore- 
going extract shows that he was already engaged in making 
microscopic observations at least three years earlier, and when 
we remember that he made all his microscopes and lenses with 
his own hands it seems certain that he must have begun his 
studies whilst his first wife was still alive.’ 

By the end of the XVII Century, when he had been 
demonstrating the scientific possibilities of the microscope 
for more than 25 years, Leeuwenhoek was actually the 
only earnest microscopist in the whole world. It is a 
remarkable fact that in all his later life he had no rivals 
and hardly a single imitator. His observations excited 
the greatest interest—but that was all. Nobody seriously 
attempted to repeat or extend them. ‘The superexcellence 
of his lenses, combined with the exceptional keenness of 
his eye, killed all competition. As early as 1692, Robert 
Hooke, discoursing on “the Fate of Microscopes”’,’ says 
that they “‘are now reduced almost to a single Votary, 
which is Mr. Leewwenhoek; besides whom, I hear of none that 
make any other Use of that Instrument, but for Diversion and 
Pastime”’:’ and he adds later that the microscope at that 

* Schierbeek (1929). 

* The only evidence that Cornelia was a highly-educated female appears 
to be (1) that her father was a clergyman; (2) that her brother was a 
doctor; and (3) that she once signed her name “ Swalmia” (instead of 
Swalmius) on a legal document—which has been taken to prove that she 
knew Latin. There is no evidence, however, to show that she changed the 
gender of her patronymic on her own initiative: and it seems to me unlikely 
that women were less dependent on their male relatives and friends 250 
years ago than they are today. 

° It is not known with certainty when L. began making “ microscopes.”’ 
The recent statements by Garrison (1921, p.835) in a learned work 
(1673. Leeuwenhoek makes microscopes”’), and by Mrs Williams-Ellis 
(1929, p.13) in a juvenile broadcast (1660. Leeuwenhoek has made 
hundreds of microscopes’’), are equally misleading and gratuitous guesses at 
the date. 

* Published by Derham (1726) in Hooke’s Phil. Expts. é Obss. 

® Ibid., p. 261. 


date ‘‘is become almost out of Use and Repute: So that Mr. 
Leeuwenhoek seems to be the principal Person left that culti- 
vates those Enquiries. Which is not for Want of considerable 
Materials to be discover’d, but for Want of the inquisitive 
Genius of the present Age.” ’ These remarks were not due to 
the circumstance that Hooke was growing an old man, and 
therefore lawdator temporis actv: they are supported by all 
scientific publications of the period. 

It is often stated’ that Leeuwenhoek was elected a Fellow 
not only of the Royal Society but also of the Académie des 
Scrences of Paris. The date of his election is variously given 
(usually 1697), and it is also sometimes stated that he wrote 
a number of letters (usually said to be 26) to this other learned 
and royal Society. But no authority is ever quoted for such 
statements, and Leeuwenhoek’s name is not included—so far 
as I have been able to ascertain—in the lists of Membres de 
l’ Académie published prior to the reconstitution of this body 
(1699). Moreover, all the ‘“ Letters from Leeuwenhoek” in 
the Journal des Scavans appear to be merely extracts or quota- 
tions in French from the Philosophical Transactions. I must 
confess, however, that I have not searched all the early 
publications of the Académie properly—the task appearing 
somewhat unprofitable. 

As I have not had access to the archives of the Académie 
des Sciences—the only present source of authoritative inform- 
ation—I have sought the help of my friend Professor F. Mesnil, 
Membre del’ Académie, who has very kindly instituted inquiries 
on my behalf. Asa result he tells me in a recent letter:* “I 
have had the Archives of the Academy of Sciences searched 
for information about Leeuwenhoek, and I have been shown 

* Ibid., p. 268. 

* e.g. by Richardson (1885), De Toni (1923), ete. No reference to the 
subject is made by Halbertsma, Harting, Haaxman, or any reliable Dutch 

* Cf. Fontenelle (1709). Ornstein (1928) gives the history of the old 
Academy (p. 139 sq.) and enumerates the early members (pp. 146, 156, 159). 
Christiaan Huygens was the only original foreign member, though several 
associate members (including Hartsoeker) were appointed later (1682). In 
Godin’s Table Alphabétique the name of L. does not occur, nor is it included 
in the elaborate tabulation of De Candolle (1885, p. 224 sq.). 

* Letter dated 21 November 1930 (translated). 


the manuscript record of the proceedings of the meeting held 
on 4 March 1699, at which each member ‘nominated his 
correspondents’ (correspondant in the etymological sense of 
the word). A physician, Burlet, nominated Leeuwenhoek— 
‘well known by virtue of what he had been able to observe by 
the use of the microscope.’ One may therefore say that 
Leeuwenhoek was a ‘correspondant’ of the old Académie des 
Sciences: his name also figures in some printed lists. Was he 
informed of this officially? No letter of thanks from him is 
in existence, nor is there any manuscript of his elsewhere in 
our Archives.” 

I conclude, therefore, that Leeuwenhoek was “ nominated” 
as a “corresponding member”—but never elected a full 
Member—of the Académie in 1699, and probably without his 
knowledge: for I can find no reference to the subject in any 
of his own letters, and there appear to be no extant letters of 
his, either published or in manuscript, addressed to Burlet or 
to the Academy or to any other member thereof (except 
Huygens). In any case, the event was without influence upon 
his activities. No scientific society except the Royal Society 
enrolled him as a member during his lifetime, though many 
have honoured him since his death.’ His name is forever 
ae to the Royal Society of London, and to that Society 

As soon as his discoveries became famous, Leeuwenhoek 
was visited by all manner of people who wanted to look through 
his glasses. The list of celebrities who went to see him is a 
long one, and has been drawn up more or less completely and 
accurately by various writers.” I need not give it here: for 
nobody believes nowadays that scientific truth depends upon 
literary or political authority or royal assent. Leeuwenhoek 
himself—being a common man—naturally felt flattered when a 
King or Queen of England, an Emperor of Germany, or a Tsar 
of Russia called upon him. It impressed his fellow-citizens and 
advanced his reputation, but he frankly confessed (in one of 
his letters to Magliabechi) that he was bored by such interrup- 
tions, and preferred to be left in peace to carry on his work. 

" Cf. Harting (1876). The statement that L. was a Fellow of “ the Royal 
College of Physicians in London” (Nieuwenhuis, 1859) is an error due, 
apparently, to confusion of this body with the Royal Society. 

* e.g. Halbertsma (1843), Haaxman (1875), etc. 


As a sample of the recorded royal visitations I will only 
mention the famous interview with Peter the Great—which 
took place in 1698, and is noted by all biographers of this 
renowned Russian monarch.’ The circumstances were recorded 
by van Loon in the following words: ’ 

The Tsar’s departure from The Hague was made in a 
canal-yacht passing by Delft, where he inspected with 
very great attention the fine arsenal of the States of 
Holland, and caused the boat to be stopped before the 
powder-magazine’® of the States-General, nearby Delft: 
and he sent two gentlemen of his retinue to the celebrated 
Antoni van Leeuwenhoek, to bid him come to see him, 
with his incomparable magnifying-glasses, on one of the 
freight-ships in his train: and the Tsar would gladly have 
gone himself to see him at his own house, had it not been 
that he was apprehensive of the crowds, which he desired 
to avoid. Leeuwenhoek repaired to His Majesty, and had 
the honour of showing him among other remarkable 
discoveries, through his particular glasses, the marvellous 
circulation in the tail of an eel; which so delighted the 
Prince, that in these and other contemplations he spent 
no less than two hours, and on taking his leave shook 
Leeuwenhoek by the hand, and assured him of his special 
gratitude for letting him see such extreme small objects. 

Peter I spoke Leeuweuhoek’s language fluently (if not 
grammatically)—having picked it up by fraternizing with 
Dutch seamen and shipbuilders. He mixed with all classes of 
people whilst in Holland and England, and had an insatiate 
curiosity to see things for himself. (It is recorded that the 
words which fell from his lips most frequently were ‘“ Dat wil 

' ¢.g. Barrow (1896), p. 67. 

2 Translated from van Loon (1731). This description is trustworthy ; 
for van Loon knew L. personally, and may well have heard the story from his 
own lips.—On v. Loon see p. 80, note 2, infra. 

> After the dreadful explosion of the former magazine inside the town (in 
1654), it was rebuilt well outside the walls—in the direction of Rotterdam 

(i.e. to the south): so Peter must have passed through Delft before he sent 

back to summon L. into his presence. Cf. p. 28 supra. 


ik zien”’..) Consequently, we may suppose that his interview 
with Leeuwenhoek in the canal-yacht on the outskirts of 
Delft was somewhat informal, and more satisfactory both to 
the exhibitor and to his audience than some other like meetings 
which required the presence of an interpreter. It is probable 
that Leeuwenhoek, on this occasion, presented the T’sar with 
some of his microscopes*—including his instrument for 
examining the circulation in the tail of an eel: for at a later 
date some similar apparatus of his manufacture was brought 
back to Holland from Russia.’ 

What manner of man was this “ celebrated Leeuwenhoek ”’ ? 
Unfortunately we get little direct information from the writings 
of his contemporaries. Kings and princes, philosophers and 
physicians and men of science, statesmen and clergymen, and 
even common men, went to see him and looked through his 
wonderful glasses: but few indeed left any written record of 
what they saw, or of their impressions of the man himself. 
Nevertheless, there are some extant descriptions of 
Leeuwenhoek by people who actually interviewed him, though 
only two are of any real importance. One of these is contained 
in a manuscript letter written by a young Irish doctor, 
Thomas Molyneux, who waited upon him early in 1685 on 
behalf of the Royal Society; the other is a lengthier printed 
account by one von Uffenbach, a German, who paid him a visit 
in 1710 when he was already a very old man. But all the 
records are interesting, and I shall therefore give them at 
length. Here isthe first—that of Molyneux,’ whose autograph 
letter is still preserved by the Royal Society. I give it word 
for word, as he wrote it, though I take the liberty of expanding 

1 “T want to see that.” Tsar Peter was evidently the father of “ the 

man from Missouri.”’ 
* As he did to our Queen Mary II (ef. p. 317 infra). 

° Discovered and recorded by Haaxman (1875), p.35. lL. never sold or 
gave away microscopes to ordinary people. 

* Thomas Molyneux (1661-1733), physician and zoologist, was brother 
of William Molyneux the mathematician and writer on dioptrics. Thomas 
was at Trinity College, Dublin, where he took his M.D. degree in 1687. He 
became a Fellow of the Royal Society in 1686, President of the College 
of Physicians of Ireland in 1702, Professor of Medicine at Dublin University 
in 1717, and was madea Baronet in 1730. For further details of his life see 
the Dict. Nat. Biogr. (art. by Norman Moore). 


the contractions in the original manuscript for typographical 
reasons and for the convenience of the modern reader: ' 

I have hitherto delay’d answering your last, because I 
could not give You any account of Myn Heer Leeuwen- 
hoeck, but last week I was to wait uppon him in Your 
name: he shew’d me several things through his Micro- 
scopes, which ’tis in vain to mention here, since he him- 
self has sent You all their descriptions at large. as to 
his Microscopes themselves, those which he shew’d me, 
in number at least a Dozen, were all of one sort, consisting 
only of one smal Glas, ground, (this I mention because ’tis 
generaly thought his Microscopes are blown at a Lamp, 
those I saw I’m sure were not) placed between two thin 
flat Plates of bras, about an Inch broad & an Inch & } 
long ; in thees two Plates there were two Apertures one 
before, the other behinde the Glas, which were larger or 
smaler, as the Glas was more or less convex, or as it 
macnify’d; just opposite to thees Apertures on one side was 
placed sometimes a Needle, sometimes a slender flat body of 
glas or opaque” mater as the occasion requir’d, uppon 
which, or to it’s apex, he fixes whatever object he has to 
look uppon, then holding it up against the Light by help of 
two smal scrues he places it justin the Focus of his glass 
and then makes his observations. Sutch were the Micro- 
scopes which I saw, and thees are they he shews to the 
Curious that come and vizite him, but besides thees he told 
me he had an other Sort, which no Man living ever look’d 
through setting aside himself, thees he reserves for his own 

1 MS.Roy.Soc., No. 2445; M.1.103, dated from Leyden, 13 February 
1685 [N.S.]. This letter has been printed previously, with slight inaccuracies 
and amended spelling, by Birch (Vol. IV, p. 365). It was addressed to 
Francis Aston, then Secretary of the Royal Society, and was read at the 
meeting held on.11 February 1685 [0.S.]—not Feb. 4 (an impossible date) 
as it appears in Birch, who here wrongly combined the proceedings of two 
different meetings. 

> In translating this letter—from Birch—Haaxman has made a slip. 
He renders “ opaque” as “ doorschijnende ’’—instead of ondoorschijnende, as 
he should have done. See Haaxman (1875), p.13, lin. penult. 







private Observations wholy, and he assur’d me they per- 
form’d far beyond any that he had shew’d me yet, but 
would not allow me a sight of them, so all I can do, is 
barely to belive, for I can plead no experience in the mater. 
as for the Microscopes I looked through, they do not 
magnify, mutch, if any thing, more, then several Glasses I 
have seen both in England & Ireland: but in one 
particular I must needs say they far surpas them all, 
that is in their extreme clearness, and their representing 
all objects so extrordnary distinctly. for I remember 
we were in a dark rome’ with only one Window, and the 
sun to, was then of a that,’ yet the Objects appeerd more 
fair and clear, then any I have seen through Micro- 
scopes, tho the Sun shone full uppon them, or tho they 
receved more then ordnary Light by help of reflectiv 
Specula or otherwise: so that I imagine tis chiefly, if not 
allone in this particular, that his Glasses exceeds all 
others, which generaly the more they magnify the more 
obscure they represent the Object; and his only secret 
I belive is making clearer Glasses, and giving them a 
better pollish then others can do. I found him a very 
civil complesant man, & douptless of great natural 
Abileties; but contrary to my Expectations quite a 
stranger to letters, master neither of Latin French or 
English or any other of the modern tongues besides his 
own, which is a great hindrance to him in his reasonings 
uppon his Observations, for being ignorant of all other 
Mens thoughts, he is wholy trusting to his own, which 
I observe now and then lead him into extravagances, 
and suggest very odd accounts of things, nay sometimes 
sutch as are wholy irreconsilable with all truth. You 
see Sir how freely I give You my thoughts of him 
because You desired it. 

2.€., room. : 
“of a that’? = off of that, i.e. off the window—not on, or shining 

through it. 


A little later Molyneux wrote again to the Society, and 
gave a few further particulars—evidently in reply to a request 
for additional information. From this letter, dated from 
Leyden, 16 March 1685, I extract the following’: 

The Glasses Mr Lewenhoeck shew’d me magnified 
Objects no more then several other glasses I have seen 
before, & therefore discover nothing but what may easily 
be seen by help of other Microscopes, so an account of 
them would be no ways satisfactory; ’tis only his owne 
privat Glasses which make those more then ordnary 
discoverys. I never heard he sold those glasses of his 
more common sort; but I sha’nt returne suddenly into 
England, for I designe, to have stayd some while in 
France, & perhaps visite Italy before that time, so I 
ca’nt serve You in this particular.” 

When Thomas Molyneux visited Leeuwenhoek in 1685 he 
was probably accompanied by his elder brother William S10 
the latter has left a record of a similar visit—buried in a book 
on optics, and consequently not generally known—which 
affords some confirmation of the foregoing account. William 
Molyneux’s words are as follows *: 

The Heer Lewenhoeck of Delft in Holland, had lately 
apply’d himself with great Diligence to the use of 
Microscopes: of which Instrument he thinks he has a 
better kind than was ever yet known. When I visited 


1 MS.Roy.Soc., No. 2446, M.1.104. Printed by Birch, Vol. IV, p. 384. 
The letter was read at the meeting of the Royal Society on 1 April 1685 
[O.8.]. I expand the contractions again, but otherwise give the exact words 
of the original. 

2 T take it that “this particular’ was a request to Molyneux that he 
should endeavour to buy some of L.’s glasses for the Society. 

§ William Molyneux (1656-1698). He was B.A. of Trinity College, 
Dublin, and a “ philosopher” and mathematician. Elected F.R.S. in 1686— 
the same year as his brother (though owing to the confusion of “old style” 
and ‘‘ new style” dating, apparently a year earlier) : entered Middle Temple, 
1675: M.P. for Dublin University, 1692 and 1695. For his life see the 
Dict. Nat. Biogr. (in which the dates of election to the Roy. Soc. are given 
wrongly for both brothers). 

“ W. Molyneux (1692), p. 281. 



this Gentleman at Delft, he shew’d me several that indeed 
were very curious; but nothing more than what I had 
ordinarily seen before; being composed only of one single, 
very minute Glass-Sphere or Hemisphere,’ placed between 
two very thin pierced Laminae, or Plates of Brass, and 
the Object was brought to its due distance before the 
Glass by a fine Screw: But for his best sort, he beg’d our 
Excuse in concealing them. The Observations he has 
made with his Glasses are Printed in several Letters of 
his in Dutch ; but for the most part, they are to be found 
dispers’d in the Philosophical Transactions. 

There is a more illuminating reference to Leeuwenhoek in 
a letter written by Constantijn Huygens jun. to his brother 
Christiaan in the year of Molyneux’s visit: and as it illus- 
trates Leeuwenhoek’s extraordinary jealousy in guarding his 
microscopes, is may be quoted here. Constantijn junior, in 
this epistle, tells his brother that he has just seen one Willem 
Meester * (a skilled Dutch mechanic), who had recently been 
with the Landgrave of Hesse* to interview Leeuwenhoek. 
Says Constantijn : * 

He [Meester] had been with him [the Landgrave] to 
Leeuwenhoek’s, who wouldn’t show him any of his 
microscopes except those which he shows to everybody ; 
whereof the little glasses had, at least, a focal distance 
equal to the width of the back of a knife. And when the 
Landgrave had asked him whether he could obtain some, 
of his manufacture, he answered with much pride that he 

* This is an error: for L.’s glasses were neither spherical nor hemi- 
spherical, but ground biconvex lenses—as Thomas Molyneux correctly 

* There are many other references to Meester in the Huygens corre- 
spondence. He appears to have accompanied the Prince of Orange in his 
campaigns. Cf. Huvr. Compl. de Chr. Huygens, Vol. VII, p. 439 note. 

* Karl, Landgrave of Hesse-Cassel (1654-1730), an amateur of science. 

* Printed in @uvr. Compl. de Chr. Huygens, Vol. 1X, p.38, No. 2408. 
5 Nov. 1685. The original MS. is in the Leyden Library, and is in 
French—from which I translate. Constantijn Huygens jun. (1628-1697) 
was elder brother of Christiaan (1629-1695), both being sons of Constantijn 
sen. (1596-1687). 


never gave any to anybody, nor did he intend to do so: 
and that if he were ever to submit to that, he would then 
soon be the slave of everybody; with other expressions of 
the like sort. When he had shown two or three of his 
microscopes, he took them away, and went to look for as 
many others; saying that he did this for fear lest any of 
them might get mislaid among the beholders, because he 
didn’t trust people, especially Germans: and he repeated 
this two or three times. O what a brute!’ 

Another person who has left a brief contemporary account of 
Leeuwenhoek and his microscopes—professedly from personal 
knowledge—is the Rev. Jean Cornand de la Crose. This 
gentleman was a French protestant refugee, who fled to 
Holland after the revocation of the Edict of Nantes and later 
settled in England, where he was received into the Anglican 
Church.” In the year 1693 he published in London a curious 
monthly magazine* in imitation of the Philosophical Trans- 
actions: and in its May number he presented his readers with 
an English translation* (neither complete nor accurate, 
though written in a language which gives no cause for 
complaint) of Leeuwenhoek’s famous letter’ on the capillary 
circulation of the blood —the first version to appear in English. 
At the end of this he added :” 

Mr. Leeuwenhoek being so deservedly famous in the 
learned World, the Ingenious will undoubtedly be glad to 

* These final words are in Italian in the original. Cf. note 3 on p. 50. 

? But little is now known of de la Crose (alias Croze seu Lacroze). His 
own Memoirs etc. supply some information regarding his career, however, and 
a few further details may be found in Agnew (1886), Vol. II, p. 270, and the 
Nouv. Biogr. Gén. (Hoefer), Vol. XXVIII [s.v. Lacroze] . 

* Memoirs for the Ingenious [etc.]. 1698. This work is now extremely 
rare. Only one volume appeared: and an attempted continuation (The 
Universal Mercury) expired with its first number in January, 1694. 

* Ibid., Letter XIX, p. 145. 

° Letter 65. Tothe Royal Society. 7 Sept. 1688. Published (complete) 
in Dutch and Latin works: not in Phil. Trans. A full modern English 
translation (with Dutch original reprinted) will be found in Opuscula 
Selecta Neerlandicorum, Vol.1I, p.38 (Amsterdam, 1907), and a mutilated 
bit of this in Fulton (1930). 

° Mem. Ing., p. 152. 



have an account of him. He is about 50 years of age,’ but 
has already imployed 15 or 20 years in Observations as 
curious as these, which I have here related. His Parents 
designed him for a Chyrurgeon, which Profession he has 
exercised some time with Honor.’ And as he rightly 
conceived, that Anatomy was the foundation of that 
useful Art, and that Microscopes were highly serviceable 
to acquire the knowledge of it, he applied himself not only 
to perfect those that were already in use, but even to 
invent new ones, in which he has succeeded to admiration, 
having discovered amongst other things more kinds of 
invisible Animals, than the World before him knew there 
were visible ones: and withal made an anatomical descrip- 
tion of many of them. The perfection to which he has 
brought his Microscopes, has atforded him great light. 
For they are not big and cumbersom tools, as the ordinary 
ones ; but light and portable, consisting only of a glass 
or two at the end of a small and short tube,’ so that he 
may manage them, and apply them to the object, as easily 
as his own Hyes. And what is still more wonderful is, 
That tho his Glasses magnify the Objects far beyond any 
I have seen, yet they do not darken it.* To which if it 
be added, that he is an able Surgeon, and has made it his 
chief business during many years to dissect and view little 
Animals, Plants, Seeds, Eggs, Saps, and the like, his 
surprizing discoveries will become more credible. I know 
some are apt to imagine, that this curious Observer of 
Nature imposes at least upon himself, in several things 

* In May 1693 L. was, of course, in his 61st year. Perhaps de la Crose 

was reporting his recollection of the time when he was himself resident in 

* This is an extraordinary mistake: but no more remarkable or inex- 

plicable than that made by one of L.’s own distinguished modern fellow- 
countrymen (de Groot, 1910), who calls our hero “ physicist and surgeon of 
Haarlem”! (ef. p. 352 infra). 

An evident error. 

* These words confirm what T. Molyneux wrote in 1685. Cf. p. 58 



which appear to them undiscernible. But as to the 
matter of fact he relates, I dare answer for his sincerity, 
having myself tried his Microscopes, viewed several things 
through them, and found them conformable to his relations. 
Besides, he is very free to let Objects be viewed through 
his Glasses, and to communicate his Observations to 
Gentlemen of Learning and Credit, especially Travellers: 
but he has made so many of them at all seasons and times 
of the year, that the Thousandth part cannot be examined 
by those that repair to him on that account. ‘There is a 
Volume of his Observations printed in Latin, some of 
which are inserted in the Philosophical Transactions, and 
I have by me some other’ very curious, which I shall 
publish in due time.’ 

The last important contemporary record is Uffenbach’s® 
well-known account of his visit to Leeuwenhoek in 1710. It is 
entertaining enough; but chiefly because of the fatuous com- 
ments of this complacent German diarist, who was so satisfied 
of his own superiority that he would be horrified if he could 
hear that his condescending notes on our poor Dutch draper 
are now the chief thing of interest in his tedious memoirs. 
This is what he wrote: * 

On the 4th December [1710] we’ went in the morning 

* From other references, it appears that de la Crose possessed a copy of 
the Dutch edition of L.’s letters of that period. 

* A few further observations on the circulation of the blood were published 
by de la Crose, but nothing else. 

* Zacharias Conrad von Uffenbach (1683-1734) was a German jurist, 
town-councillor of Frankfort, and a keen collector of books, coins, and 
“curiosities”. His Travels were published posthumously in 1753-54 (ed. 
Schelhorn), and much of his insignificant correspondence has also appeared 
in print. His life is prefixed to his memoirs, and will also be found in the 
Allg. Dtsch. Biogr. 

* Translated from the German of Uffenbach (1754), Vol. ITT, pp. 349-360, 
with immaterial omissions which are duly indicated. The full description 
is too long-winded to give here in its entirety. In my translation I have 
left the Latin words as Uffenbach gave them, in order to preserve his 
pedantic style of expression. His mistakes are too evident for comment. 

° “We” apparently denotes Uffenbach and his brother. 




to see the famous observator microscopicus, Leeuwenhoek,’ 
by whom . . . we were most courteously received. 
The only daughter that he has, a person of about forty,” 
led us first into an antechamber, and told us that her 
father, though he had discovered many new things with 
his microscopia in recent years, did not wish to publish 
any more of his observations during his lifetime, because 
of the affronts he had suffered, presumably in the writings 
of others ; for he has now and then been ridiculed for the 
odd views expressed in his own writings, and has been 
accused of seeing more with his imagination than with 
his magnifying glasses. Mr. Leeuwenhoek is a man of 
seventy-eight, but still hale and hearty, save that he 
cannot much use his feet. We were surprised to find him 
not at all shaky, and he still has almost incomparable 
eyesight, though he taxes his eyes greatly with his 
observations. He showed us the following experiments : 
First, the circulation of the blood, very fine and clear, in 
the tail of a quite little flounder (which is one of the 
greatest delicacies among sea-fish). He was not only of 
opinion that where the blood runs upwards, these are the 
arteries, and where it runs downwards, the venae (of 
which I justly doubted whether such a sweeping assump- 
tion were allowable?), but also he maintained that 
it is the venae and not the artervae which pulsate. 
He also insisted that he could see with the naked 
eye that the pulse at the wrist beats downwards 
rather than upwards. Methinks, however, that herein 
Mr. Leeuwenhoek does but show his ignorance of 
anatomy; for the structure of the arteries sufficiently 
proves that the valvulae in them undoubtedly cause the 
pulse-beat, whereas the blood merely flows along and 

‘ His name is spelled “ Leuwenhoeck” by Uffenbach throughout—a 

mistake which I have taken the liberty of correcting wherever it occurs in 
his narrative. 

* Maria was really aged 54 at this time; and consequently Uffenbach’s 

statement is an unintentional compliment on her personal appearance. 


through the venae, which have no valvulae. Besides, it 
is surely impossible to distinguish whether the pulse at 
the wrist beats downwards or upwards? But this by 
the way.—Mr. Leeuwenhoek then cut off with a knife a 
small bit from a mussel,’ such as they are here wont to 
eat, and showed us that all its parts were in a continuous 
motion ; just as a snake apparently continues to move 
itself for a long time when freshly hacked to pieces with 
a switch. In both cases this is due to the vital spirits, 
which seek to escape, and so bring about the movements. 
Afterwards Mr. Leeuwenhoek cut a mussel in two through 
the middle, in order to show us how the eggs and young 
mussels are generated. He also showed us certain black 
dots, which he maintained were young mussels in their 
black shells; but we couldn't take them for such, being 
unable to distinguish them. He also cut the gut of a 
mussel in two, and showed us, by means of his micro- 
scopium, a great mass of sand in it, which the mussels 
presumably take in with the slime in which they live. 
Mr. Leeuwenhoek considered, and not unjustly, that this 
sand serves for the formation of the shells of their young 
ones, just as hens and other birds readily eat sand and 
lime for the sake of their egg-shells. He wished also to 
show us the circulation of the blood in an eel, only the 
creature was too big and black. Mr. Leeuwenhoek makes 
this experiment with an instrument which . . . is 
simple, large, and not at all convenient. The one made 
by Mez in Amsterdam, with a camera obscura, is better ; 
with this one you are dazzled by the light and the glass. 

Mr. Leeuwenhoek showed us the circulation of 
fee blood very well with this machine, though it was 
somewhat troublesome to manipulate, and would be even 
worse for making observations lasting over a long time, 
because you have to put the side of the mcroscopwwm, 
where the lens is, against your forehead, and look 

1 No doubt L. showed the ciliary motion on a portion of the gill of 
Mytilus—as he well knew how. 




upwards through the tiny glass; which, after some time, 
would become tiresome. Mr. Leeuwenhoek afterwards 
fetched some cases, in each of which were two 
microscopia’ . . . likewise of quite a simple structure. 

Each of these microscopia had a_ particular 
curiosity stuck before it; but we saw the following: 
First, in tubulo capillari, upwards of thirty small young 
oysters 7m spiritu vint. These could be seen quite clearly, 
and had the perfect form and structure of old and big 
oysters. . . . We inquired how he introduced these 
young oysters into his capillary tubes, which he 
explained in the following fashion: He cuts off the 
gut of an oyster, takes some of the stuff that is in it 
on a pen-knife, and smears it on his thumb-nail; he 
then pours a drop of spirits of wine upon it, and applies 
the capillary tube thereto, whereupon the spirit runs up 
the tube of itself, through the pressure of the air, and 
takes the little oysters along with it, they being commonly 
present in the substance that is in the beard or the gut 
of the old oysters. He uses spirit for this purpose in 
order that they may not so easily become foul, which, 
being fish, they only too readily do, as happened indeed 
formerly with him, when he used only water. This ex- 
periment is one of the finest and most curious that we 
saw at Mr. Leeuwenhoek’s. He showed us further a 
“maggot”, as they are called, supposed to grow in the 
port of the nose. . . . Through another microscopium he 
showed us a sand-grain, which looked like the finest 
crystal with facettes. ... In another microscopium he 
had, on a bit of glass, a particle of gold, which he had 
previously dissolved in aqua regia and then precipitated : 
this appeared just like a little gold tree, and exceeding 
pretty. . . . Next, Mr. Leeuwenhoek showed us, through 
another microscopiwm, the scale of a fish, whose structure 

* These may have been the silver instruments bequeathed to the Royal 

Society. Cf. p. 96 wnfra. 


was certainly wonderful. . . . At this point Mr. Leeuwen- 
hoek remarked that he must show us that men also have 
scales. Accordingly, he took a pen-knife, and scratched 
his arm several times; then took a glass tube and with it 
scraped several times the place that he had scratched. 
He then let us look at this tube through his mzcroscopiwm, 
whereupon many little particles, like scales, were visible 
lying upon it. These the good man takes to be scales, 
which a human being is provided with in order that the 
extremities of the nerves may not be injured, as also to 
prevent his sensations being too strong ; for if the nerves 
were not so guarded, he would be unable to stand pain, or 
irritation, nor could he do any work. It is surely quite 
sufficient, however, that man is clothed with several skins, 
as is known from anatomy, and he has no need of scales 
like a fish: and what the good Mr. Leeuwenhoek takes for 
scales are really only the particles, or scurf, from the outer- 
most skin, which are commonly present, especially in per- 
sons of adry habit, and particularly on the head, and which 
are cast off from the cuticwla as it dries up and peels off 
under the influence of the external air, but chiefly through 
the internal heat of the body, though it always forms 
anew underneath. Mr. Leeuwenhoek showed us further 
the eye of a fly, which appeared very remarkable under 
the microscopium, and had the appearance of veritable 
hexagona lying alongside one another; which Mr. 
Leeuwenhoek considers actually are eyes, and consequently 
makes flies into something better than so many Arguses ; 
for he is of opinion that a fly, according to his view, has 
more than a hundred, nay, more than a thousand, eyes ; 
which is only one of this good man’s extraordinary notions, 
which seem wont to have more of ingenuity than founda- 
tion. Further, he showed us the wing of a fly, which also 
appeared very wonderful . . . The sting of a fly appeared 
also very singular .. . Finally, Mr. Leeuwenhoek showed 
us his cabinet, in which he had at least a dozen little 
lacquered boxes, and in these quite a hundred and fifty of 
the little cases before mentioned, in each of which there 



lay two microscopes of the small sort. As we marvelled 
at this large store, we asked him whether he never sold 
any? as we would gladly have possessed ourselves of 
some: but he said no, he would sell none in his lifetime. 
He was also very secret about his work, and how he did 
it: but we drew one thing and another out of him with 
all manner of questions. Thus, when we asked him 
whether all these mzcroscopia were identical? he said 
they were all ground in the same grinding-cup, but 
nevertheless there was a difference between the various 
lenses, and as regards those ground last in any cup, 
indeed, a great difference..... When we further 
inquired of Mr. Leeuwenhoek whether he ground all his 
lenses, and did not blow any? he denied this, but 
displayed great contempt for the blown glasses. He 
pointed out to us how thin his microscopia were, com- 
pared with others, and how close together the laminae 
were between which the lens lay, so that no spherical 
glass could be thus mounted ; all his lenses being ground, 
contrariwise, convex on both sides. He also had some 
microscopia with double glasses, which, though they were 
double, and the lenses separated inside at their proper 
distance, presumably by another lamina, were nevertheless 
not much thicker than the simple ones. Notwithstanding 
that these are pretty troublesome to make, they yet are 
not much better than the simple ones, excepting that 
they magnify a little more; but only a little, as Mr. 
Leeuwenhoek himself confessed. As regards the blown 
glasses, Mr. Leeuwenhoek assured us that he had 
succeeded, after ten years’ speculation, in learning how 
to blow a serviceable kind of glasses which were not 
round. My brother was unwilling to believe this, but took 
it for a Dutch joke*; since it is impossible, by blowing, 
to form anything but a sphere, or rounded end. Yet one 
cannot sufficiently marvel at Mr. Leeuwenhoek’s great 

' A pleasing German expression for a falsehood. 


diligence and industry, both in the making of observations 
and in the grinding of lenses, as also in the manufacture 
of the mechanical parts for his microscopia; albeit the 
latter are simple, and badly worked, and for the most 
part roughly fashioned, even the silver not being filed 
smooth in a single one of them. We much wanted to ask 
him why he made so many microscopia, though he would 
not sell any ; but we feared we might get only a Dutch 
answer.. Presumably jealousy lest anybody should get 
hold of microscopes of his pattern, during his lifetime, is 
chiefly at the bottom of this; but there is also some self- 
interest, in that his daughter will one day be able to sell 
them so much dearer, if they cannot be got during his 
own lifetime.” As we were going, both this extraordinary 
man and his daughter earnestly intreated us to tell no 
one that we had been to see him, or seen anything 
there; for the reason that he is old, and tired of being 
pestered, especially by people who are not true lovers of 
learning. .... We were told not only in Delft, but also 
by many foreigners who had waited upon him in vain, 
that he would see no one, still less show people anything : 
and we were therefore greatly rejoiced that we saw so 
many curious things at the house of this extraordinary 
old man. 
One final account of Leeuwenhoek by a man who met 
him must, unfortunately, be mentioned. It was given by 
Hartsoeker,’ an envious fellow-countryman, and was obviously 

*7.e. none: another German pleasantry. 

* As a comment on this unjust remark, it may be recalled that L.’s 
microscopes were not put up for sale until 1747—two years after Maria’s 
death. Cf. p. 320. 

* Nicolaas Hartsoeker (1656-1725), physicist, astronomer, and mathe- 
matician: son of Christiaan Hartsoeker (1626-1683), a minister of the 
reformed Church. He had a variegated career, which is recorded in Dict. 
Sct. méd. (1822), V, 85; N. Ned. Biogr. Woordenb. (1924), VI, 718; and 
elsewhere. In Cwvres Compl. de Chr. Huygens (VIII, 58n) it is stated that 
Hartsoeker was born on 25 March 1654: but this is contradicted by his own 
statement in the Hzt. crit. (1730), p. 43, where he himself gives the date as 
26 March 1656. 


inspired by dislike and jealousy. I shall not quote his 
words, as they have already been repeated by Haaxman 
(1875) and others, and are not worthy of further consideration. 
It is now abundantly evident that Hartsoeker had wronged 
Leeuwenhoek, and therefore hated him; while on his side 
Leeuwenhoek despised Hartsoeker and treated him with 
contempt. All this can be read in their various references 
to one another.” When he was very young, Hartsoeker—who 
had visited Leeuwenhoek with his father, and had been 
shown or had heard of the discovery of the spermatozoa— 
went to Paris, and there tried to palm off this discovery as 
his own. He did not succeed—though there are still 
credulous or ignorant writers who accept his claims *—and 
when the facts became known he was reduced to silence. 
More than forty years later, when Leeuwenhoek had at last 
died, Hartsoeker attempted to blacken his character and 
reasserted his own priority *: but he himself died before his 
malicious remarks were published (1730), so that he was 
denied the final satisfaction of kicking Leeuwenhoek’s corpse 
in public. Hartsoeker was a man of undoubted ability, but 
quarrelsome and arrogant and in every way the very 
antithesis of Leeuwenhoek. He attacked and found fault 
with everybody he envied—not only Leeuwenhoek, but also 
Newton, Leibniz, and even Christiaan Huygens (who had 
befriended him)—and his foolish criticisms and _ personal 
complaints are now best consigned to the oblivion which 
they deserve. On his own confession he was virtually 
turned out of the house by Leeuwenhoek when he last 
attempted, by a subterfuge, to visit him. I _ shall 
therefore treat Hartsoeker likewise here,’ and give him 

"See Hartsoeker (1730), Extrait critique, passim. 

* See L.’s letters and Hartsoeker’s publications passim: also Cuvres 
Compl. de Chr. Huygens—especially Vol. VIII. 

* Cf. Martin (1764), Launois (1904), ete. 

“ Hartsoeker’s claims to the discovery of the spermatozoa have recently 
been critically considered and correctly assessed by Cole (1930). 

° I must add, however, that I have carefully and impartially read all the 
available evidence concerning Hartsoeker’s relations with L. Consequently 
I am well aware that much already written on this subject is incorrect, 
though it seems to me unnecessary to discuss all the data here. French 
writers especially—doubtless influenced by Fontenelle—have, in general, 


no further publicity. Leeuwenhoek’s own last comment 
on him was’: 

It has come to my ears that Hartsoeker hasn’t much 
of a reputation among the learned: and when I saw that 
he laid claim to untruths, and was stuck-up, I looked 
into his writings no further. 

The foregoing quotations show what some of Leeuwenhoek’s 
contemporaries thought about him: but the best description 
of himself is that unconsciously written by his own hand. His 
own letters are filled with autobiography. On almost every 
page he tells us of his thoughts, his feelings, his everyday 
actions: so that we can now form a very clear and probably 
correct picture of his personality. But it was all done quite 
naturally and ingenuously; for he had no thought, when he 
was writing, that be was often revealing himself rather than 
some ‘“‘mystery of nature”. He sets down his views— 
frequently quite mistaken and even ridiculous views—with 
childish and charming simplicity, and he has no feeling of 
embarrassment in telling the Royal Society the most intimate 
details about his blood, his sweat, or his urine; or about his 
sicknesses or his habits or his little vanities: because he 
always imagines that he is recording matters of scientific 
interest, and he knows by instinct that in registering his 
observations he ought not to withhold any data which may 
possibly have a bearing upon his findings. Yet he always 
presents his results in a way which, despite the imperfections 
of his language and his lack of scientific education, is a model 
for all other workers. He never confuses his facts with his 
speculations. When recording facts he invariably says “I 
have observed . . .”, but when giving his interpretations he 
prefaces them with “but I imagine...” or “I figure to 
myself...” Few scientific workers—or so it seems to me— 
have had so clear a conception of the boundary between 
observation and theory, fact and fancy, the concrete and the 

given Hartsoeker far more credit than he deserves: Dutch writers are better 
informed. (Fontenelle’s Hloge of Hartsoeker will be found reprinted at the 
beginning of the latter's posthumous Cowrs de Physique, 1730.) 

' Send-brief XVIII, 28 Sept. 1715, to Leibniz (Brieven, Vol. IV, p. 170). 


But every reader of Leeuwenhoek’s letters must form his 
own opinion of the man himself. Some have been—and will 
be—revolted by his “‘grossness” and “ vulgarity”: others 
will continue to delight in his very “ commonness”’, and will 
even find in it something meritorious. For my own part, I 
confess that I enjoy his most commonplace sayings, because 
they satisfy my own craving for simplicity and common sense 
in all things—especially in those called “scientific”. When 
Leeuwenhoek makes casual “asides”? about the most trivial 
affairs of his life, it does not offend me: it rather helps me to 
understand him. I like to hear that he generally drank coffee 
for breakfast and took tea in the afternoon, or that he shaved 
himself twice a week and got a rash on his hands when he sat 
in the sun: and I even laughed uproariously when I first read 
the letter in which he gravely told the Royal Society— 
evidently giving it as a tip to the Fellows—that he found it 
advisable to drink a great many cups of extremely hot tea on 
rising if he had had a drop of wine too much the night before 
with a friend. But when he speaks of his little white long- 
haired pet dog, or of his parrot “ which is moulting,” or of his 
horse “‘ which is a mare”’, or incidentally remarks that he was 
wont to throw bread to the sparrows when the snow was on 
the ground, I feel that I really know the sort of man he was. 
Little touches such as these bring the heavy-featured blue- 
eyed Hollander of Verkolje’s painting very vividly before my 
mind's eye, and explain—in an inexplicable and inexpressible 
manner—his crude but inspired discoveries in protozoology 
and bacteriology. They make me want to find excuses for all 
his many mistakes. It is so obviously his works—not his 
words—which count. I do not suppose that he ever read any 
writings of his great contemporary John Bunyan: but had he 
done so he would certainly have understood what Bunyan 
meant when he wrote: ‘‘ Yea, if a man have all knowledge, he 
may yet be nothing, and so consequently be no child of God. 
When Christ said, Do you know all these things? And the 
Disciples had answered, Yes: He addeth, Blessed are ye if ye 
do them.” * 

* John Bunyan (1628-1688), the immortal English tinker. I quote 
from the first edition of the Pilgrim’s Progress (1678), p. 113—written in 
Bedford jail. 


Our Leeuwenhoek was manifestly a man of great and 
singular candour, honesty, and sincerity. He was religiously 
plain and straightforward in all he did, and therefore sometimes 
almost immodestly frank in describing his observations. It 
never occurred to him that Truth could appear indecent. 
His letters, accordingly, are full of outspoken thoughts which 
more “scientific ” writers would hesitate to put on paper: and 
to the modern reader this is, indeed, one of his particular 
charms—for he is far more childlike and innocent and 
“modern” than any present-day writer. In his own similar 
language he must often have said the beautiful prayer of 
Thomas More: “‘ Our Lorde kepe me continuallye true faithfull 
and playne, to the contrarye whereof I beseche hym hartelye 
never to suffer me live.’’* 

But Leeuwenhoek—like all honest workmen—took a pride 
in his work. He jealously guarded what he believed to be 
true, though always willing to change his opinions when 
cogent arguments were advanced against them. All studious 
readers of his letters will be able to call to mind a score or 
more of places where he confesses his scientific faith. It is 
impossible to quote all these passages here, but a few extracts— 
taken at random—will illustrate this aspect of his personality. 
Writing to the Royal Society in 1692 he says’: 

I well know, Most Noble Sirs, that the propositions I 
come to make, and which I’ve sent you from time to time, 
do not all agree with one another, but contradictions are 
to be found among them: so I will only say once more 
that ‘tis my habit to hold fast to my notions only until 
I’m better informed, or till my observations make me go 
over to others: and I’ll never be ashamed thus to chop 
and change. 

ee ee 

™ Tn one of Sir Thomas More’s letters written in prison to his daughter 
Margaret. See More’s Utopia ete., ed. Sampson (1910) p.281. More was 
born in 1478 and beheaded on 6 July 1535. His Utopia was first published 
at Louvain in 1516. It is unlikely that L. had ever read it, though the 
first Dutch translation appeared in 1653. 

2 Letter 74, 12 August 1692. MS.Roy.Soc. Cf. Brieven, Derde Vervolg, 
p- 507. Not published in Phil. Trans. 


A little later, in a letter to the Rev. George Garden’ he 
wrote °: 

I must say to you, as I’ve oft-times said already, that 
‘tis not my intention to stick stubbornly to my opinions, 
but as soon as people urge against them any reasonable 
objections, whereof I can form a just idea, I’ll give mine 
up, and go over to the other side: and especially because 
my efforts are ever striving towards no other end than, 
as far as in me lieth, to set the Truth before my eyes, to 
embrace it, and to lay out to good account the small 
Talent that I’ve received*: in order to draw the World 
away from its Old-Heathenish superstition, to go over to 
the Truth, and to cleave unto it. 

The following characteristic passages * are all from the last 
published series of Letters—the Send-brieven, written by 
Leeuwenhoek to various people at various dates : 

I have said before now, that, if ever I came to err in 
my discoveries, I would make open-hearted confession 

In the observations aforesaid I have spent a lot more 
time than many people would believe: yet I made them 
with pleasure, and paid no attention to people who say to 
me ‘‘ Why take so much pains?” and ‘“‘ What’s the use 

* George Garden (1649-1733), a Scottish divine, and minister at 
Aberdeen till 1701—when he was deposed for writing an “ Apology’’ for 
Antoinette Bourignon, the religious fanatic who assisted in Swammerdam’s 
downfall. Garden was not a Fellow of the Royal Society. 

* Quoted in Letter 81, to the Royal Society. 19 March 1694. Cf. 
Brieven, 4de Vervolg, p.671-2. There is no extant MS. of this letter, 
which was sent to the Society by L. in the form of a printed proof-sheet 
and was not published in the Phil. Trans. 

* The reference is obviously to Matth. XXV, 25 sq.—the parable of the 
talents. Li. does not here use the biblical words, but his own have a strong 
flavour of the Bible—as was only meet, in writing to a clergyman. 

* I translate from the Dutch versions, as nearly as I can: for the flavour 
of the originals is almost wholly lost in the more formal Latin translations. 

> Send-brief II, p. 16. 


of it ?’’ because I don't write for such folks, but only for 

Hereupon I must remark that it don’t seem strange to 
me that there are still some who won’t accept of my 
propositions regarding generation : for novelties oft-times 
aren’t accepted, because men are apt to hold fast by 
what their Teachers have impressed on ’em.” 

A certain very understanding Gentleman in our Town, 
who had been reading my printed Letters, said to me: 
“Teeuwenhoek, you’ve got the truth, but it won't be 
received in your lifetime”. And therefore it doesn’t 
strike me as odd, that I meet with contradictions during 
my life.” 

Yet how the Tuba Fallopiana can perform any kind of 
sucking is to me inconceivable: and though I must confess 
I’ve often heard Doctors and Physicians talk about 
things that seem to me to have no rhyme or reason, yet 
of nothing worse than generation by an egestock and 
the Fallopian tube. ‘I'would have been better if they'd 
said “it’s a secret quality”: for of course it would have 
been too silly for learned people just to say “we don’t 
know ’’.* 

I see well that I can’t bring many learned gentlemen 
to believe in my true discoveries and also in my proposi- 
tions: but herein I find more to comfort me than for 

Be EEE ee 

' Send-brief II, p. 22. 

? Send-brief XVIII, p. 166. 
® Send-brief XVIII, p. 168. 
* Send-brief XXIII, p. 211. 


quarrel, if I have but the luck (as I have) that many great 
men also do accept of my discoveries.’ 

I’m well aware that these my writings will not be 
accepted by some, as they judge it to be impossible to 
make such discoveries: but I don’t bother about such 
contradictions. Among the ignorant, they’re still saying 
about me that I’m a conjuror, and that I show people 
what don’t exist: but they’re to be forgiven, they know 
no better.” 

I well know there are whole Universities that won’t 
believe there are living creatures in the male seed : but 
such things don’t worry me, I know I’m in the right.’ 

These sayings are typical of Leeuwenhoek, though they 
are but random samples: I will not rob his readers of the 
pleasure of finding for themselves many another equally good. 
Almost every letter he ever wrote contains some remark 
which throws light upon his character—especially his last 
letters, written when he was very old. ‘These, as might be 
expected, are crammed with the reminiscences of a lifetime 
spent in the solitary contemplation and interrogation of 
Nature. All his long life he kept on asking questions of 
Nature—whose own favourite child he was—in common 
colloquial old-fashioned Dutch, and trying in his simple way 
to understand her answers made in a pure and perfect language 
which we still cannot interpret correctly. But it is for the 
poet—not for the scientist or historian—to portray our Child 
of Nature in communion with his Mother. I cannot even 
attempt the task, and must now merely chronicle the last 
chapters in a prosaic life packed with the stuff of scientific 
and artistic dreams. 

In 1707, when he was in his 75th year, the Royal Society 
sent to ask after Leeuwenhoek’s health—being anxious because 

" Send-brief XXX, p. 304. 
* Send-brief XXXII, p. 317. 
* Send-brief XLI, p. 405. 







Enlarged from a miniature portrait by J. Goeree (1670-1731), inset in the 
engraved title-page of the last volume of the Letters (1718). 

facing p. 76 

ra aiw isis juli 

ath ae 7 ne 

Pe reece rit eng uf 
re YTS (Hin ry : 
_ re 
wut ; ‘ 



they had received no letters from him for nearly a twelvemonth. 
(He had evidently ceased to write merely because the Society 
had not acknowledged his three previous communications.) 
To their inquiries he returned the following reply, addressed 
to John Chamberlayne’: 

I received your acceptable Letter of the 20th of March, 
deliver’d by your Nephew the 29th of April last, wherein 
you are pleased to say, that the Honble. Royal Society 
are very much concerned that they have had no account 
of my health for a great while, and that you had com- 
manded your Nephew to wait upon me and desired me to 
let you know how I did. 

Your Nephew delivered your Letter to my Daughter, 
but I was not at home, and since that time I never saw 
him again. I am thankfull for your Civilities. 

As to my health, thanks be to God, as long as I sit still 
I am without any pain, but if I do but walk a little I have 
pains in my leggs,” but that is, I think, caused by former 
colds and because they have carried my body so long. 

In other letters of this period we hear of various other 
visits paid to Leeuwenhoek in his old age by Fellows of the 
Royal Society and other people. Most of these visitors— 
notwithstanding Uffenbach’s statement *—seem to have been 
kindly received, and entertained with divers microscopical 
sights (especially the capillary circulation in the tail of a little 
eel). His reasons for refusing to see people occasionally were 
given by himself; and in this connexion the following un- 
published passages from two otherwise published letters are 

* From Letter dated 17 May 1707. To J. Chamberlayne, F.R.S. MS. 
Roy. Soc. Unpublished. This interesting letter is peculiar in that the 
original is in English. As no Dutch or Latin version accompanies it, and 
as it is apparently written on L.’s own gilt-edged letter-paper (such as he 
used at that time), I infer that the translation was made in Delft, by a 
friend, and that the letter was sent in the form in which it now survives. 
I transcribe the words of the MS. exactly, merely expanding a few 
contractions in the original.—F'or Chamberlayne, see p. 270, note 2, infra. 

" Cf. Uffenbach’s statement, p. 64 supra. 
* Cf. p. 69 supra. 


worth quoting. Writing to the Royal Society early in 1710 
Leeuwenhoek remarks ’*: 

I have received by the hands of Mr Stuart’ the six 
several T'ransactions, for which gift I am most deeply 
thankful, and wish I had the ability to do the Honourable 
Society some service in return. 

Mr Hans Sloane * recommended Mr Stuart to me, in his 
letter, as a curious Gentleman who has travelled through 
many countries ; and the same Gentleman had two other 
Scottish gentlemen in his company, all of whom I gladly 
received, and so will I do all those who have an introduc- 
tion from Mr Sloane. But if I should receive everyone 
who comes to my house, or tries to come, I should have 
no freedom at all, but be quite a slave. 

The second letter was written to James Petiver,* who 
unsuccessfully attempted to see Leeuwenhoek in 1711. The 
passage in question reads as follows’: 

* Translated from Letter dated 14 January 1710. MS.Roy.Soc. Original 
in Dutch. The rest of this letter, in English translation, appeared in Phil. 
Trans. (1709 [1710]), Vol. XXVI, No. 323, p. 444: not published in Dutch 
or Latin collective works. 

? Alexander Stuart, M.D.; born about 1673, and died in 1742. He was 
elected F.R.S. in 1714. As a young man he journeyed to the Far East as a 
ship’s surgeon. He entered the University of Leyden, being then 36 years 
old, on 14 Dec. 1709, and graduated M.D. there on 22 June 1711. After- 
wards he settled in London, where he attained a position of considerable 
eminence in the medical profession. For these and other biographical 
details about Stuart—who is not mentioned in the Dict. Nat. Biogr.—I am 
indebted to Dr W. Bulloch, F.R.S. 

* Sir Hans Sloane, M.D. (1660-1753): Secretary of the Royal Society 
from 1693 till 1712, and President from 1727 to 1741. His varied scientific 
and other activities are too well known to require further notice here. For 
his life see the Dict. Nat. Biogr. 

* James Petiver (1663 ?-1718), a London apothecary. He was elected 
F.BR.S. in 1695, and wrote much on plants, shells, and other subjects. His 
vast collections were purchased by Sloane, and incorporated in his own. 
His life will be found in the Dict. Nat. Biogr., where it is recorded that “ in 
1711 he went to Leyden, mainly to purchase Dr Hermann’s museum for 
Sloane’’. Cf. also Green (1914), who speaks highly of some of Petiver’s 

> Translated from Letter dated 18 August 1711. MS.Roy.Soc. Original 


I have received your Letter of the 2nd of August anno 
1711, wherein you are displeased at not being welcomed 
at my house. I beg you please not to take it ill, seeing 
that we send off everyone who tries to visit me, unless 
they have some sort of introduction. 

I willingly received Mr Alexander Stuart Medicina? 
Doctor, who presented me with the dissertation for his 
degree, and had with him your T’ransactions, and a letter 
from Mr Hans Sloane, and brought with him also two 
other Gentlemen; and I let them see sundry observations 
of mine. Since that time I would gladly have received 
you on divers days; and if you had kept by you the letter 
from Mr Hans Sloane, you would not have missed a 
friendly entertainment at my house. And you were sent 
away especially because you were not known, and because 
some 8 or 10 days earlier no less than 26 people came to 
see me within four days, all of them with introductions 
(except a Duke and a Count, with their Tutor): which 
made me so tired, that I broke out in a sweat all over. 
This being so, I beg that you will not take it amiss 
in me, that, to my great sorrow, you were turned away. 
If my poor old legs could have stood it, I would have 
looked you up in Rotterdam. 

In 1716, when he was in his 84th year, the University of 
Louvain officially honoured Leeuwenhoek by sending him a 
medal in recognition of his work. ‘This incident—which 
corresponds roughly, at the present time, with the conferring 
of an honorary degree—is not uninteresting, and may there- 
fore be noted here with Leeuwenhoek’s own comments. 

in Dutch. The rest of this letter was published (in English) in Phil. Trans. 
(1711), Vol. XXVII, No. 331, p.316. It is not in the Dutch or Latin 
collective works. 

So in original: “ medicina ” (for medicinae) is not a lapsus calami but 
a mistake on L.’s part—for he knew no Latin, and makes similar mistakes 

* Stuart’s thesis for his medical degree at Leyden was entitled ‘‘ De 
structura et motu musculari’’—a subject which greatly interested L. It 
was published in 1711 (4°. Leyden), and afterwards reprinted more than 


Among the minutes of Mr J. van der Werff, onetime 
notary public of Delft, the following entry has been found’: 

Upon this day the 3rd of June 1716 appeared before 
me, Jacob van der Werff, notary within the Town of Delff, 
in presence of the witnesses hereinafter named, Mr. 
Gerard van Loon, brewer at the Brewery called This 
Cross-grained World, within this town; and declared that 
by him present was duly received an epistle bearing the 
superscription: J’o the Highly-honoured and Far-famous 
Mr. ANTHONY LEEUWENHOEK, etc. at Delff, under cover ; 
together with a little silver medal, having graven upon the 
obverse thereof the lhkeness of the said Mr. Leewwenhoek 
encircled by the words “ANTHONY LEEUWENHOEK 
fteg: Societ: Angl: Membr:” and upon the reverse thereof 
the Town of Delff in the background,’ with the subscrip- 
tion “in tenut labor, at tenuis non gloria” (from Virgil *) : 
being enclosed in a little horn box, lined inside with 
velvet, and in a little bag of woven gold, sent to the 
appearant (as he explained) by Mr. ANTHONY CINK,’ Pro- 

* Quoted by Servaas van Rooijen (1904, p. 381), from whose transcript 
I translate. I have not seen the original. 

* Gerard van Loon (1683-1758), born at Delft: historian, lawyer, and 
numismatist, as well as brewer. He is now best known for his monumental 
work on Dutch historical medals (4 vols. folio, 1723-1731). Cf. N. Neder. 
Biogr. Woordenb. (1930), VIII, 1070. L.’s Send-brief XXII (16 May 1716) 
was addressed to v. Loon, and deals with hops—a subject of mutual interest, 
as L. indicates: for he notes that v. Loon’s mother owned a brewery, while 
his (Leeuwenhoek’s) grandfather and great-grandfather were brewers, and 
his grandmother the daughter of a brewer, ‘so that my forefathers handled 
much hops.” Cf. p. 20, supra. 

* And in the foreground, I may add (since this explains the motto), a 
beehive with bees actively at work collecting honey from a plant bearing 

* Georg. lib. IV, v. 6—the famous poem on the oeconomy of bees. The 
application to L. is both obvious and apt. 

° Antony Cinck (1668-1742), a Hollander born at ’s-Hertogenbosch 
(Bois-le-Duc), was a remarkable man; and in addition to his qualifications 
noted above was also sometime professor of pedagogics at Louvain, and of 
rhetoric at Liége. Being a Jansenist, he was later excommunicated by the 
Archbishop of Mechlin and fled back to Holland, where he died (at 
Dordrecht). Cf. N. Nederl. Biogr. Woordenb. (1924), VI, 300; and S. van 
Rooijen (1904). 


fessor of Philosophy, Canon of Liége, Prebendary of St. 
Peter's at Louvain, President of the College of Cranen- 
donck,' etc. etc., with written accompaniment and urgent 
request that the appearant should be pleased to take upon 
himself the charge of delivering the foresaid letter, medal, 
box, and bag, to the said Mr. Leeuwenhoek, on behalf of 
Mr. Cink and the other Professors of Medicine and 
Philosophy at Louvain, as an honourable gift and recogni- 
tion of their appreciation of his (Mr. Leeuwenhoek’s) 
never yet properly appreciated and celebrated discoveries 
in Natural Philosophy: which foresaid letter, medal, box, 
and bag, according to the charge aforementioned, on 
receipt thereof from the appearant, hath been handed 
over to Mr. Leeuwenhoek. 

Appeared likewise before us, notary and witnesses, the 
oft-mentioned Mr. Anthony Leeuwenhoek, who declared 
that he had received each several article, furthermore 
thanking Mr. van Loon. 

This document was signed by van Loon, Leeuwenhoek, 
the two witnesses, and the notary. The silver medal itself 
can still be seen in the Municipal Museum at Delft, and has 
been depicted by van Loon’* and by Haaxman.’ The former, 
in his description of it, mentions that he himself handed it 
over to Leeuwenhoek in person “in a ceremonious manner.” 

Leeuwenhoek’s own acknowledgement of this honour is 
contained in a letter * which he addressed on 12 June 1716 to 

* One of the 43 colleges at Louvain: cf. Ray (1673), p. 13. 
2 G. van Loon (1731), Vol. IV, p. 223. 

* Haaxman (1875), p.116. The reproduction is not good, and the Latin 
motto contains a misprint. 

* Send-brief XXV. Printed in Brieven (1718), Vol. IV, p.220: and in 
Latin in Op. Omn. (Epist. Physiol.), Vol. IV, p.219. [The Latin version 
of the passage here quoted is not a good translation of the original.] A 
previous communication with Cinck (through van Loon) is to be found in 
Send-brief IX, 24 Oct. 17138. 



‘Professors Cink, Narrez,’ Rega,’ and other Gentlemen of the 
College of The Wild Boar”’.’ In this letter he wrote : 

By the hand of Mr. Gerard van Loon, the advocate, I 
have received an obliging letter from Your Excellencies, 
dated 24 May last, and a purse made of cloth-of-gold ; 
wherein lieth, in a little black box, a silver medal showing 
my bust on one side of it, and an emblem with the Town 
of Delft in the distance on t’other. 

Along with this, in further explanation and as a 
dedication, was enclosed a certain Latin Poem of praise,’ 
overflowing with elegant expressions; but notwithstand- 
ing my praises be therein sung very high, yet the poet’s 
cleverness deserveth still higher praise for screwing them 
up to such a pretty pitch: and when I think on the 
flatteries expressed in your letter, and in the poem, I 
don’t only blush, but my eyes filled with tears too, many 
a time: especially because my work, which I’ve done for 
many a long year, was not pursued in order to gain the 
praise I now enjoy, but chiefly from a craving after 

————— eee 

1 Ursmer Narez (1678-1744), M.D. Louvain (1718), in his day a 
distinguished man. After devoting himself to religious studies in his youth, 
he became lecturer on philosophy in the University; and after qualifying 
as licentiate in medicine (1706) was successively professor of botany, 
anatomy and surgery, and institutes of medicine. He was also head of the 
hospital at Louvain. Cf. Biogr. Nat. Belg. (1899), XV, 471. 

® Henri-Joseph Réga (1690-1754), M.D. Louvain (1718). Entered the 
University of Louvain—where he was born and died—in 1707, and became 
licentiate in medicine in 1712. He was afterwards professor of chemistry 
(1716), anatomy (1718), and clinical medicine (1719), and is an influential 
and outstanding figure in the history of medicine in Belgium. Cf. Brogr. 
Nat. Belg. (1903), XVII, 842. 

> °t wilt Swijn (= Het wilde Zwijn or Het Varken). There were formerly 
four principal schools of philosophy in the University of Louvain—each 
having a particular name and symbol. The members of © The Wild Boar ’”’ 
or “ Collége du Porc”’ took theirs from a sign-board opposite the house 
where they first assembled in 1430. Cinck and van Loon (who was his 
pupil) both belonged to this ‘‘ college” or “ pedagogy’, whose fellows were 
known by the apparently uncomplimentary title of “ Porkers” (Porcenses). 
Cf. Ray (1673, pp. 15-17), and S. v. Rooijen (1904). 

* Composed by J. G. Kerkherdere: vide infra. 


knowledge, which I notice resides in me more than in 
most other men. And therewithal, whenever I found out 
anything remarkable, I have thought it my duty to put 
down my discovery on paper, so that all ingenious people 
might be informed thereof. 

In conformity with the foregoing sentiments, our octo- 
genarian microscopist here proceeds to record still further 
discoveries which need not now detain us. But in his next 
published letter, which was addressed to the writer! of the 
panegyric poem just mentioned, he makes a remark which is 
worth quotation. In this letter, after giving thanks for the 
Latin verses in his honour, Leeuwenhoek adds” 

I always know myself well enough to ee that I’m 
not worthy of the hundredth part of the expressions you 
make about my poor work: for it springs only from an 
inclination I have to inquire into the beginnings of 
created things, in so far as ‘twas ever possible for me to 
do so. 

And he then delivers to the uninterested Kerkherdere a 
lengthy disquisition (occupying some 18 printed pages) on his 
latest botanical observations. 

Another letter, written a few months later in the same 
year, gives some particulars of Leeuwenhoek’s health at 
this period (1716). This letter was sent not to the Royal 
Society nor to Louvain but to Dr Abraham van Bleys-wyk °* 

"Den Heere J: G: Kerkherdere, syner Keyserlyke en Koninglyke 
Mayjesteyts Historicus.’’—Jan Gerard Kerkherdere (1677-1738) of Louvain 
was a theologian, grammarian, and classical scholar. By all accounts he 
possessed a special aptitude for writing Latin verses, which he was able to 
produce with great facility on all ceremonious occasions. He was appointed 
historiographer to the Emperor Joseph I in 1708. See N. Nederl. Biogr. 
Woordenb. (1924), VI, 878; and Biogr. Nat. Belg. (1886-7), IX; also Nouv. 
Biogr. Gén. (Hoefer), sub voce “ Kerckherdére.”’ 

* Translated from Send-brief XXVI. 22 June 1716. Published in 
Brieven (1718), Vol. IV, p. 232; and in Latin in Op. Omn. (Epist. Physiol.), 
Vol. IV, p. 230. 

* Abraham van Bleyswijk [alias Bleiswijk, Bleyswijck, etc.] was M.D., 
and lector anatomicus at Delft—as L. himself informs us. (Cf. Send- brief 
XXXVI. 26 May 1717.) He was a pupil of Boerhaave, and took his 


of Delft —whom he calls his “nephew” '—and is as 

When I had the honour of being visited by yourself 
and Professors Boerhaave * and Ruysch,’ who took delight 
in some of my discoveries; as Mr Boerhaave was taking 
his leave, and wishing me health and long life, I made 
objection to him that I couldn’t go on much longer; 
because, in view of my advanced age, my insides (meaning 
the guts) were just about worn out. But as it was time 
for the Gentlemen to be off, my further reasonings were 
interrupted: wherefore I now take the liberty of 
explaining my last attack to you. 

'Tis now above a sennight ago that I was very short of 
breath, which was accompanied by a tightness of the 
chest,’ pain (as I imagine) in the diaphragm and in the 
stomach, and a rising of the gorge. Accordingly, I 
ordered them to fetch me some warm water, to help me 

degree at Leyden with a dissertation “qua in praxi felicitas mechanicorum 
vindicatur’’ (4°. Lugd. Bat. 1708). Little else now appears to be known 
about him: he is not mentioned in N. Nederl. Biogr. Woordenb. or by 
Hirsch. Banga (1868, pp. 614,869) who also notes the foregoing particulars 
adds that Bleyswijk helped L. in his anatomical studies—a statement for 
which he gives no evidence, and which may be questioned. It seems 
probable that Abraham was a kinsman of Dirk Evertsz. v. B. who published 
the well-known description of Delft (1667). 

‘ Neef—a term which (like “ cousin” in English) did not at that date 
necessarily denote the relationship now implied. It was commonly bestowed 
on any kinsman. 

> Send-brief XXVII, 17 Sept. 1716. Printed in Brieven (1718), Vol. IV, 
p. 254: Op. Omn. (Epist. Physiol.), Vol. IV, p.250. No MS. and not in 
Phil. Trans. I translate the whole letter—relying chiefly on the Dutch 
printed version. 

* Herman Boerhaave. See p. 296, note 6, anfra. 

* Frederik Ruijsch (1638-1731), the celebrated anatomist and injector : 
Professor at Amsterdam. For his life see Banga (1868, p.514 szq.), 
Scheltema (1886), and N. Nederl. Biogr. Woordenb. (1914), III, 1108. He 
was elected F.RB.S. in 1715 (not 1720, as stated by Banga). 

> benautheyt Dutch ed. pectoris angustia Lat.—The “shortness of 
breath’ and “ tightness of the chest’’ here mentioned in the originals are 
vulgar expressions usually denoting asthma. Cf. Blankaart (1748) and 
Gabler’s Woordenboek. 


to be sick: and no sooner had I drunk the warm water, 
than I vomited, and that very easily. Soon after I was 
sick again with great violence, so that the food I brought 
up (as they told me) came out of my mouth and nose: 
but I knew not what I was doing. When I came to 
myself, I examined the stuff I had cast up: and I found 
it was not only the food I’d taken the evening before, but 
even what I’d had the previous mid-day. 

When I let my thoughts run regarding this, I imagine 
that the cause of my attack was as follows: The 
membranes, whereof the coats of the guts are composed, 
are so made that they have divers motions, in order to 
push the chyle, that’s in them, onwards towards the 
outfall‘: to bring which about, a continual increase of 
contraction” of the guts is needful, as long as there 
remaineth any chyle in ‘em: and if there be no chyle in 
the guts, they stay at rest. And in promoting this 
pushing-on of the chyle, the bile, which is poured into 
the gut, helps not a little: for the bile congeals in the gut 
into sharp particles. 

During this attack I was very costive, just as I had 
been for a good month previous, notwithstanding I was 
taking only bland food: and a full three days passed ere 
the chyle brought me to stool.° 

I’m therefore sure there was no proper motion in my 
guts, and that the gut lying next the stomach was stuffed 
with food, or chyle; wherefore the stomach was also stopt 
with food: for if the guts don’t lie still, the stomach 
strives to unburden itself of the food that’s entered it, by 
squeezing itself together: so that I’m sure the stomach, 


" afgang orig. [=evacuatio intestinorum]. The Latin translator evaded 

the word, merely saying that the chyle is pushed ‘‘deorswm’’. Chyle = chyme: 
see note 5 on p. 284 infra. 

* Meaning peristalsis. 
* This paragraph is so paraphrased in the Latin version that its import 

is rather obscure. The Dutch is particularly frank. 


in a well set-up body, must so contract, that how little 
food soever be in it, ’tis ever full. 

The stomach being now overladen with food, and 
unable to get rid of it because the gut is full of chyle; 
and these long strainings of the stomach being against 
its natural shape: it arouses, by its strivings, a pain in 
the midriff (which they call the Diafragma), which is 
thereby hindered in its continual motion; which also 
stirs up a second pain. The midriff accordingly presseth 
on the lung; and thereby, the lung is prevented from 
performing its office. And this being so, there must 
follow a great tightness and a great vomiting: and such 
violence is done to the body, to the stomach as well as to 
the guts, that the chyle in the gut is thereby pushed 
onwards; so that there followeth a motion in the gut 
itself. And, as I imagine, when the gut is full up, the 
gall-bladder can’t empty its bile into the gut, yet with 
these onpushings of the chyle it pours a great quantity 
of bile into the guts; therefore on the day when this 
happens, four or five stools are brought off, whereas on 
the other days there ensueth a constipation. 

You have here the feeble notions I’ve hammered out 
of my last distemper. Pray take it not amiss that I take 
upon myself to argufy about it. 

The foregoing lines are not only an interesting record of 
Leeuwenhoek’s bodily condition in his 84th year, but also a 
typical example of his own particular system of physiology. 

References to his age and his infirmities become more 
numerous with advancing years. He continues to make and 
record observations and speculations, and to promise more: 
but he often begs the Royal Society to make allowance for his 
senescence, and sometimes qualifies his promises with expres- 
sions such as “if my health permits”.' At the end of 1717 
Leeuwenhoek thought his own end was near; and he therefore 
inscribed a “last letter” to the Society, as an envoy to the 

* met gesondheijt, ete. 


final collective edition of his works. Concluding this letter 
he wrote’: 

Methinks these will be the last observations I shall 
be able to send to you honourable Gentlemen; because 
my hands grow weak, and suffer from a little shakiness, 
which is due to my far advanced years, a good 85 having 
passed by me. And so I send you with this my deep 
thankfulness, because in the year 1679* you were so kind 
as to elect me, quite beyond my competence, a Fellow 
of the most worthy College of the Royal Society ; and to 
send me a Diploma, together with two letters from the 
Secretaries of the Society, which likewise made known 
to me my election, by all the votes of the Fellows, then 
gathered together at a very full meeting.” 

I thank you also for the Philosophical Transactions, 
which Your Excellencies have been so good as to send 
me from time to time. 

For all these honours and gifts aforesaid, I herewith 
convey to you my gratitude once more. 

But the end was not yet. After writing the foregoing 
lines, Leeuwenhoek lived for nearly six years more ; and 
during this period he sent the Society no less than 18 more 
letters (including 2 posthumous epistles), containing a variety 
of new microscopical discoveries. In a postscript to one of 
these letters he says *: 

1 From Letter dated 20 November 1717. To the Royal Society. There 
is no MS. of this letter in the Roy. Soc. collection. It was not published 
in the Phil. Trans., but was printed in both Dutch and Latin : Send-brieven 
(1718), No. XLVI, p. 451; Opera Omnia [Epist. Physiol.] (1719), Vol. IV, 
No. XLVI, p. 437. I translate from these published versions.—It is 
remarkable that Miall (1912, p. 201) and several other students of L. have 
assumed that this was really his last letter. 

? 1680, according to present-day reckoning (N.S.). Cf. p. 48 supra. 

* Cf. p. 48, note 6, supra. 

‘From Letter dated 24 January 1721. To the Royal Society. MS. 
Roy. Soc. (The postscript is in L.’s own hand, but the letter itself is in 
different handwriting.) Original in Dutch—from which I translate. An 
English version of this letter was published in Phil. Trans. (1721), 

Vol. XXXI, No. 367, p.134. It is not in the Dutch or Latin collected 


I humbly beg that you will make some allowance for 
me, my years having mounted to a great height. A 
certain Gentleman, visiting me a few months ago, 
besought me to make some further discoveries; adding, 
that those fruits which ripen in the autumn last the 
longest. And this is now indeed the Autumn of my 
days, for they have today mounted up to 88} years. 

Yet only three months later he wrote with characteristic 
confidence—after describing some observations on the structure 
of peas :* 

"Tis my intention to inquire into these marvellous 
structures more narrowly, just for my own amusement.’ 

Next year, after communicating other discoveries, 
Leeuwenhoek sent the Society still further observations 
together with the following unpublished personal remarks’: 

The learned Dr James Jurin, Secretary of the Royal 
Society,’ writes to me from London in your name, on 
22 Feb. 1724, with so many expressions of satisfaction at 
my discoveries, which I sent to your Fellows, that I stood 
all abashed when the letter was read to me; nay, my 
eyes filled with tears at all the great expressions, and 

" The same remark is made by L. in his Send-brief XXXII, 2 March 
1717, to Abraham y. Bleyswijk (printed in Dutch and Latin works): ef. 
Brieven, IV, 317. 

* From Letter dated 11 April 1721. To the Royal Society. MS. Roy. 
Soc. Printed (in English) in Phil. Trans. (1721), Vol. XXXI, No. 368, 
p.190. Not in Dutch or Latin collected works. 

* alleen voor mijn plaijsier MS. 

* Translated from Letter dated 21 April 1722. To the Royal Society. 
MS. Roy. Soc. Partially published (in English) in Phil. Trans. (1722), 
Vol. XXXII, No. 371, p.72. Not in Dutch or Latin collective works. 
Original in Dutch, in L.’s own hand—showing evident signs of senility. 

° De seer geleerde Heer Jacob Jurin, Secretaris van Hare Hoog Edele 
Heeren Vergadering MS. It is impossible to translate these merely formal 
expressions into literal English without making them appear rather 
ridiculous, and so spoiling their intention: I therefore paraphrase.—James 
Jurin (1684-1750) was a physician—sometime Fellow of Trinity College, 
Cambridge, and President of the Royal College of Physicians of London. He 
was elected F.R.S. in 1717, and became Secretary on 30 Nov. 1721. His 
life will be found in the Dict. Nat. Biogr. 


respect that they have for my work, which I accomplish 
alone by my own impulse and inclination. For no money 
could ever have driven me to make discoveries, and I’m 
only working out as ’twere an impulse that was born in 
me, and I imagine I never meet with any other people 
who would spend so much time and work in searching 
into the things of Nature. And withal I had great pleasure 
too at hearing that the learned and curious Mr James 
Jurin’s investigations have made him eye-witness of my 

The same Gentleman also said, that your Fellows very 
earnestly desired, if ’twere possible, that my observations 
should be confirmed and cleared up by repeating them, so 
that the mouth of the unbelieving might be stifled. 

On this matter I would reply to your Honourable 
Fellows, that I have indeed inquired into many things of 
one and the same nature, but not thought it needful to 
describe them all, because the one must imply the others. 
And those things that are not easy to believe, I have left 
standing for days, nay years, before the magnifying-glass, 
to let them be seen by as many people as possible; like 
the vessels in the nerves, which have lain so long before 
the magnifying-glass, that they have been all eaten up by 
that little creature the Mite.” 

By this time Leeuwenhoek was an old and sick and dying 
man. But despite his age and his infirmities he still continued 
to make observations and send letters to the Royal Society. 
In two letters, written in March and May 1723, he even gave 
the Society an account of the illness from which he suffered 
in the last year of his life. Both letters were translated into 
Latin, and they were the last he lived to sign: their Dutch 
originals are now lost. As the relevant passages are of great 
personal interest, I shall quote them at length. On19 March 

“The whole of this paragraph is ungrammatical and very loosely 
constructed in the original. 

* The two foregoing paragraphs were paraphrased—not translated—in the 
Phil. Trans., though their sense is there conveyed correctly. 


1723, after discussing the dimensions of blood-corpuscles, he 
wrote : 

This also I have to add: that notwithstanding my 
advanced age cannot but hinder my sight, yet my right 
eye, to my great annoyance, groweth somewhat dim. I 
think this comes to pass for the reason that sundry 
blood-corpuscles, floating in the crystalline humor,’ stray 
in front of my sight; some whereof being joined together 
in no or only an irregular order, with others floating 
separately, cause an appearance of little clouds* in my 
eye. Moreover, as I generally use my right eye, I 
readily shut my left eye whilst making observations, 
wherefore my eyesight is dimmer than ’twas wont to be. 

Not so long ago, to wit this last January, I was seized 
with a violent motion about that great and necessary 
organ we call the diaphragm: indeed, ’twas such that 
those present were not a little alarmed at it. When the 
motion abated, and I sought to know the name of this 
distemper, the Physician who was at hand replied that 
it was a palpitation of the heart. But I thought the 

*To Dr James Jurin, Sec. R.S. MS.Roy.Soc. Printed in Phil. Trans. 
(1723), Vol. XXXII, No. 877, p.341; not printed in Dutch or Latin 
collected works. I translate from the original Latin MS.—inscribed in an 
unknown hand (not Hoogyliet’s). 

? humor crystallinws—the old name for what is now called the “ crystalline 
lens” (cf. Blankaart, 1748, swb voce). This structure was described in 
detail, in many animals, by L.; and he knew that it was solid and stratified 
and that it contained no blood-vessels or corpuscles. Consequently, I 
cannot help thinking that in his original words—here mistranslated (?) into 
Latin—he must really have referred to the vitreows humor: which would 
obviously be nearer the truth. 

* mibeculae Phil. Trans. mnubeculae MS. The printed word is meaning- 
less, and greatly puzzled me until I discovered that it was merely a 
misreading of the original. lL. was here referring, of course, to the familiar 
entoptic phenomena called muscae volitantes—now known to arise from 
shadows cast on the retina by strands in the vitreous humor. (Cf. Brewerton, 
1930.) These appearances were first described by L. in his Letter 41, 
14 Apr. 1684, to F. Aston (Ondervind. & Beschouw., 1684, p.19; also in 
Latin editions; incomplete English translations in Phil. Trans. XIV, 790 
[ =780], and Hoole, I, 241). 


Physician was wrong; for whilst the motion lasted, 
I off put my hand on my pulse, and could feel no 
quickening of its beat. This violent motion, returning 
at intervals, lasted for about three days; during which 
time my stomach and guts ceased to perform their office 
and motion, so that I was verily persuaded I stood at 
death’s door. 

In my opinion there was some obstruction, not less 
than a crown piece in bigness,’ stopping my diaphragm. 

On 31 May 1723 Leeuwenhoek actually sent the Royal 
Society a description of the histology of the diaphragm, which 
he had meanwhile studied (in sheep and oxen) in order to 
support the opinions expressed in the foregoing letter. And 
at the end of his account of the various muscles and tendons 
and vessels observable in the midriff he added :* 

Accordingly, the oftener I recall the foresaid distemper 
which seized me last winter, and which I attributed 
mostly to my diaphragm, the more am I of opinion that 
our Physicians are mistaken when they call that 
commotion, which we sometimes feel in the region of our 
chest, a palpitation of the heart. For my part, | am 
persuaded that such palpitations arise from a disorder 
of the Diaphragm; howbeit this may be brought about 
either by a deficiency of diet, or by obstruction of those 
blood-vessels which run through the diaphragm in great 
plenty. Such an obstruction can easily excite convulsive 
motions in the tendons aforesaid; and I believe this was 
the very cause of my own complaint. 

Towards the middle of August, 1723, Leeuwenhoek had 
another seizure; and now he was indeed—as he himself 

‘non minorem nummo imperialt MS. I take nummus imperialis to mean 
a rizksdaalder (—= 2% florins), which was roughly of the size and value of an 
English 5-shilling piece. 

* From Letter dated 31 May 1723. To the Royal Society. MS.Roy.Soc. 
Printed in full in Phil. Trans. (1723), Vol. XXXII, No. 379, p.400. Not 
in Dutch or Latin collective editions. Original MS. in Latin, from which 
I translate. 


realized—at death’s door. Yet even Death’s proximity could 
not abate his scientific zeal. Boitet the publisher—who 
cannot always be trusted, but who here probably wrote from 
recent personal knowledge—has left it on record that he 
continued his researches to the very end. He says:? 

Our Leeuwenhoek, who had a sound mind in a sound 
body, felt however about a year before his death that his 
bodily powers were getting noticeably weaker, owing to 
an asthmatical chest and other symptoms: nevertheless, 
he continued his course cheerfully to the end of his life 
along the track of Science, to win a deathless name at 
last, though forsooth he had won the race long before 
during his lifetime. Six-and-thirty hours before his death, 
when his limbs were already growing numb, the fire of 
his ardour glowed still so bright, that, with lips stammer- 
ing and well-nigh stiff, he directed his thoughts to be set 
down on paper regarding a kind of sand which a certain 
distinguished gentleman, a director of the East-India 
Company, had handed over to him, to find out whether 
any gold were concealed therein. 

And this account is supported from another quarter. As 
he lay dying, Leeuwenhoek summoned his friend Dr Jan 
Hoogvliet * to his bedside, and requested him to translate a 
couple of letters* into Latin and send them to the Royal Society 
as a parting gift. The good doctor did so, and dispatched 

* Boitet (1729), p. 768—translated. Z 

* Little seems to be now known about Johannes Hoogvliet, who is not 
mentioned by Banga or Hirsch or in the N. Nederl. Biogr. Woordenb. or any 
other available works cf reference. I have been able to ascertain only that 
he was a surgeon practising at Delft, and that he once published a work on 
wounds (Konst om wonden te schouwen, etc. 8°. Rotterdam, 1749). He was 
probably a kinsman (? brother) of the poet Arnold Hoogvliet (1687-1763) of 
Vlaardingen, who wrote the panegyric poem prefixed to the Send-brieven, 
and whose father—a shipowner and sheriff—was also called Johannes. 

* On “corpuscles in the blood and in the dregs of wine” and “the 
generation of animals and palpitation of the diaphragm.’”’ Published 
posthumously in Phil. Trans. (1724), Vol. XXXII, No. 380, pp. 436-440: 
not in Dutch or Latin collective works. 


them with the following covering note from himself to the 
Secretary’ : 

Our venerable old Leeuwenhoek, being already in the 
throes of death, though none the less mindful of his art, 
ordered me to be called to him ; and raising his eyes, now 
heavy with death,’ kept asking me in half-broken words 
if I would translate these two letters out of our native 
tongue into Latin, and send them, most distinguished Sir, 
to you. In obedience, therefore, to these commands of 
so great a man, with whom I had been for some years on 
terms of most intimate friendship*, I can do no less than 
send you, most learned Sir, this final gift of my dying and 
most dear friend: hoping that these his last efforts will 
prove acceptable to you. 

I pray that the Supreme Judge of all things may long 
bless Your Excellency, and the Royal Society: Farewell. 

Leeuwenhoek’s death was first made known to the 

Fellows of the Royal Society by a letter from the minister of 
his church—the Rev. Mr Peter Gribius.* His communication 

1 MS. Roy. Soc., No. 1413; H. 3.112. Joannes Hoogvlietius to J. Jurin, 
Sec. R.S., 4 September 1723. Printed fully (except last sentence) in Phil. 
Trans. (1724), XXXII, 435. My translation is made from the original MS. 
(very clearly written in good classical Latin), whose endorsement shows that 
the letter was read at a meeting of the Society on 7 Nov. 1723 [O.S]. 

2 attollensque oculos jam gravatos morte MS. “ mij met reeds half gebroken 
oogen aanstarende’”” Haaxman (1875, p.122)—a mistranslation. 

= quo abhinc jam aliquot annos usus fueram faniliarissime MS. Haaxman, 
ioc. cit., also misconstrues these words, which do not imply that Hoogvliet 
had been accustomed to translate L.’s letters into Latin for several years. 
The expression ‘ wtor aliquo”’ means “I enjoy the friendship of someone ”: 
ef. Cicero—His Fabricius semper est wsus Oppianicus familiarissime (pro 
Cluentio, XVI, 461, 46). Moreover, no other known letters of L. are extant 
in Hoogvliet’s handwriting. 

* He styled himself “ Petrus Gribius, Ecclesiae Delphensis pastor senex.”’ 
Gribius [alias Grybius] was born at Middelburg in 1651, and died at Delft 
in 1739. He was educated in the Latin Schools of Amsterdam, Utrecht, 
and Leyden, and before taking holy orders visited Oxford and Cambridge. 
He became minister of the New Church at Delft in 1681 (Boitet, 1729, 
p. 441), and retired in 1734. Some of his sermons and essays have been 
published, and his portrait was painted by Thomas v. d. Wilt (cf. p. 345). 
Further details of his life will be found in an article contributed by F. S. 
Knipsheer to the N. Nederl. Biogr. Woordenb. (1924), VI, 634. 


has never been published, and even its existence has hitherto 
been overlooked. Yet it is a document of the greatest 
interest: for it not only announced Leeuwenhoek’s death, but 
also recorded the exact date thereof, and gave a few particulars 
regarding his last illness and the cause of his decease —as 
determined by his medical advisors. I shall therefore give 
this letter in its entirety. The original is written in Latin, 
and addressed to Dr James’ Jurin, Secretary of the Royal 
Society. Dated from Delft, 30 August 1723, it runs as 
follows > 
I venture to interrupt you, most distinguished Sir, in 
your very urgent engagements and duties, solely because 
I am moved thereto by the tears of Maria, the only 
daughter of her great father Antony van Leeuwenhoek ; 
who, while he neither feared nor desired his last day, 
peacefully concluded it upon the 26th of August; being 
then over ninety, and thus, having reached arare old age, 
neither unripe nor half-ripe, though verily more than 
mature. For ’tis with man as with pear or apple, on a 
tree laden with fruits, some whereof it letteth fall thickly 
and perforce, while others, when they be more than ripe, 
drop singly of their own accord.’ As the Poet’ elegantly 
saith : 

Kijpes ebeotaciw Oavaroto 
Moupia, ds ovK gore huyeiv Bpotov, odd’ vroAnEat.” 

" Gribius wrongly addressed him as “John” (Nobilissimo Viro Joanni 
Jurin Regiae Societati a secretis Illustrissimo). 

* MS. Roy. Soc., No. 1214; G.2.3. The translation of this letter has 
been by no means easy: for it contains several classical quotations and 
veiled allusions, and some unusual words and expressions—designed, 
apparently, to show off the writer’s scholarship. Nevertheless, its latinity 
seems not altogether irreproachable. In tracing the references to Homer 
and Statius I have been greatly assisted by Prof. D’Arcy Thompson, F.R.S. 

° The foregoing lines in the MS. are apparently a paraphrase of Cicero: 
“quasi poma ex arboribus, cruda si sunt, vi avelluntur, si matura et cocta, 
decidunt’’ (de Sen. lib. XIX, § 71 ad finem). Some modern texts read “ vix 
evelluntur,’ but Gribius’s words indicate that he was familiar with the 
older version. 

* Homer, Ilias XII, 326-7. 
° “Ten thousand fates of death do every way beset us, and these no 


Yet ’tis our duty to submit to the wise dispensations of 
God, Whom we wrongfully defraud of His rights unless 
we humbly suffer each one of ours to live and die according 
to His will. 

The notion possessed our good old man that he lay 
a-dying of a distemper of his diaphragm, though in fact 
‘twas of his lungs; and their gradual obstruction, turning 
slowly into a suppuration, reached such a pitch that he 
cast up purulent sputa and died when the lung had 
festered, on the sixth day after he took to his bed.’ So 
at least say our Physicians, who are highly skilled in 
such matters: for my part, I know nought of diseases; a 
cobbler should stick to his lasts.’ 

A little cabinet, furnished with some most select 
glasses (commonly called Mcxpocxoma*), to be given after 
his death to the Royal Society, will be sent to you within 
six or seven weeks by his daughter, as she hath informed 

Amongst us he has left a reputation truly good, and 
enshrined in the Temple of Memory, by virtue of his 
indefatigable inquiries into Nature. To you, most noble 
Sir, who hold an honorable office, and one worthy of 
your deserts, I wish many a long year of life, that for the 

mortal may escape nor avoid” (translation of Lang, Leaf, and Myers). The 
last word of the quotation is given wrongly by Gribius: it should be 
imanrvéat. (Cf. Ilias ed. Doederlein, Lips.-Lond. 1863.) 

’ Ag the foregoing lines constitute the only known record of the cause of 
L.’s death, the reader will doubtless desire to see the original words. The 
MS. says: Bonwm senem tenwit opinio se moriturum diaphragmatis vitio, 
sed pulmonum fuit, eorumque lenta obstructio sensim in suppurationem 
vergens, adeo ut phlegmata purulenta ejecerit, et suppurato pulmone obierit, 
seato postquam decubuit die. It is clear that L. died of broncho-pneumonia: 
and there is much evidence (largely unpublished) in his later letters to show 
that he had suffered for many years from chronic bronchitis. 

= ne sutor ultra crepidas MS. This familiar proverb occurs in several 
forms, and according to Pliny originated in a saying of the painter Apelles. 
Pliny’s version is © e supra crepidam sutor judicaret”’ (Hist. Nat. XXXV, 
[10]36. Fol. Genevae [1582] p. 629). 

* = Microscopes. To write the word thus in Greek—even at that date— 
was a ridiculous bit of pedantry. 


public benefit you may live to equal, or even excel, those 
grand old men of Troy.’ 

The cabinet of microscopes bequeathed to the Royal 
Society—yreferred to in the foregoing letter—-had been briefly 
described by Leeuwenhoek himself twenty-two years earlier. 
In an unpublished passage in an otherwise published letter to 
the Society he had written *: 

I have a very little Cabinet, lacquered black and gilded, 
that comprehendeth within it five little drawers, wherein 
lie inclosed 13 long and square little tin cases, which I 
have covered over with black leather; and in each of 
these little cases lie two ground magnifying-glasses 
(making 26 in all), every one of them ground by myself, 
and mounted in silver, and furthermore set in silver, 
almost all of them in silver that I extracted from the ore, 
and separated from the gold wherewith it was charged ; 
and therewithal is writ down what olject standeth before 
each little glass. 

This little Cabinet with the said magnifying-glasses, as 
I may yet have some use for it, | have committed to my 
only daughter, bidding her send it to You after my death, 
in acknowledgement of my gratitude for the honour I 
have enjoyed and received from Your Excellencies. 

On 4 October 1723, Leeuwenhoek’s bequest was duly and 
dutifully dispatched to the Royal Society by his daughter 

1 ut... Iliacos aequare senes aut vincere possis MS. This is apparently 

borrowed from the hexameter of Statius: “‘Iliacos aequare senes, et vincere 
persta”’ (Silvae, lib. II, iii, 73). I take it that by these words Gribius 
meant to say that he hoped Dr Jurin would live long enough to rival, by his 
scientific performances, the doughty deeds of the heroes of ancient Greece 
in the field of battle: but the comparison seems somewhat forced, to say 
the least. 

2 Brom Letter 140. 2 August 1701. MS.Roy.Soc. Printed (Dutch) 
in Sevende Vervolg der Brieven (1702), p. 375; and (Latin) in Opera Omnia 
(Contin. Arc. Nat.), Vol. III, p. 355. I translate from the Dutch MS. 
(Words here italicized were underlined by L. himself in the original.) 
Although this Letter was not published in the Phil. Trans., the passage 
here given was translated into English and entered in the Society’s Letter- 
books (Vol. XIII, p. 183), and this entry was long afterwards extracted and 
printed by Weld (Vol. I, pp. 244-8). 


Maria along with two covering letters. One of these was a 
formal notification in Latin from the Rev. Mr Gribius; the 
other was a simple Dutch letter from Maria herself. I shall 
give them both. 

Gribius wrote’: 

In our present scientific age, 6 Maxapirns” Antony van 
Leeuwenhoek considered that what is true in natural 
philosophy can be most fruitfully investigated by the 
experimental method, supported by the evidence of the 
senses; for which reason, by diligence and tireless labour 
he made with his own hand certain most excellent lenses, 
with the aid of which he discovered many secrets of 
Nature, now famous throughout the whole philosophical 
World: of which sacred apparatus he bequeathed no 
contemptible a share, inclosed by himself in this little 
cabinet, to the Royal Society, with no other object than 
to afford those ingenious and most erudite men a token 
of his veneration, and as a mark of his gratitude for 
having been enrolled among their learned Company. 

His Daughter (a spinster of excellent repute, who has 
preferred a single life to matrimony, in order that she 
might ever continue to attend her father) earnestly begs 
this one favour: that you disdain not to send back word 
that this little present hath not gone astray, but is come 
safe into your hands; which I likewise fully trust was 
the lot of my own letter*® written to you, in no joyful 
spirit, five weeks ago. 

I pray God, most illustrious Sir, that He suffer you 
long to continue shining as a great and singular light and 
star of the first magnitude to Philosophy. 

1 Translated from MS.Roy.Soc., No. 1215; G.2.4. Petrus Gribius, 
Eccl. Delph. pastor senex, to J. Jurin, Sec. h.S.; 4 Oct. 1723. Original in 
Latin: unpublished. 

° = The blessed (7.e. in heaven). 

° Referring to his communication of 30 August 1723-—p. 94 ante. 
From this remark it must be inferred that the Secretary of the Royal Society 
had neglected to acknowledge Gribius’s first epistle. 




Maria’s letter was very different from the foregoing. It 
made no pretensions to scientific knowledge or classical 
scholarship, and was written not in Latin but in homely, 
illiterate, and even ungrammatical Dutch. It was apparently 
dictated—not written by herself—for it is inscribed in a 
handwriting different from the somewhat shaky signature.’ 
(Maria was then 67 years of age.) But for all that it is one 
of the most beautiful and pitiful letters I have ever read— 
breathing sincerity and filial devotion in every word, and 
eloquently testifying to Leeuwenhoek’s own qualities as a 
man and father. Maria wrote’: 

Most excellent Sirs 

Instantly upon the sad death of my beloved father 
Anthonij van Lewenhoek,* I took care to have this my * 
loss made known to you by our reverenced and most 
learned pastor, Peterus Griebius’; adding thereto, that 
after the space of six weeks would be sent to the noble 
and far famed Royal Society, at London, a little cabinet 
with magnifying-glasses, made of silver wrought out of 
the mineral by my dear departed father his very self; 
which same is now sent to Your Excellencies, even as 
my late father made it up, with six-and-twenty magnifying- 
glasses in their little cases: truly in itself a poor present 
to so celebrated a Royal Society, but meant to betoken 
my father’s deep respect for such a learned Society, 
whereof my most beloved and dear Father, of blessed 

* Cf. Plate XIII. 

* MS.Roy.Soc., No. 2137; Z.6.38. Maria van Leeuwenhoek to the 
Royal Society, 4 Oct. 1723. Original in Dutch, from which the above is 
a, translation—and a poor one: for I confess myself incompetent to turn the 
pathetic but unscholarly expressions of Maria into intelligible modern 
English faithfully. 

* So spelled in MS. 

‘In the MS. the words “this my” are reiterated: “dit mijn mijn dit 
mijn’’—the second dit being scored out. Maria apparently hesitated, in 
dictating the letter, between saying “mijn” or © dit mijn”: and in her 
agitation she failed to notice that the word mijn was finally left written 

* So spelled in MS. 


bane frag ad, 
ae ne f i aes os TY 

‘UMOUY o[dulexe eos 9U}—oinjzeusis Joy SUIMOYS : (EGLT “9°90 F) 



Es ——— cay gl Baad 94 

. poring vag gheyrog oeg 
? 7, 

sg 2ehe we 



facing p. 99 


memory, hath had the honour to have been a fellow- 
member. Your most humble servitress now begs Your 
Excellencies, please to be so good as to let me have word 
whether this trifling gift is come safe into the hands of 
the far famous College, that I may rest content I have 
fulfilled my Father’s wish. 

Wherewith, most famous Gentlemen, 

your most respectful Servitress 

and my father’s Grief-stricken 

Delft, the Daughter now and hereafter 
4th October 1723 — will ever be and remains 
New Style Your humble Servant 

Maria van Leeuwenhoek 
Antoni’s daughter 

This letter needs no comment: it speaks for itself. I need 
only add here that the little cabinet of microscopes was safely 
received by the Royal Society: that it was examined and 
reported upon by the Vice-President, and by one of the 
Fellows at a later date: that it was treasured by the Society 
for a century—and then lost." In return for the bequest, the 
Council in 1724 sent Maria “a handsome silver bowl, bearing 
the arms of the Society.” ° 

Leeuwenhoek was buried in the Old Church of Delft on 
Sunday the 31st of August 1723—‘ with 16 pall-bearers and 
with coaches and tollings of the bell at 3 intervals ’ ’—and his 
grave was finally closed two days later (2 September).* He 
was first laid to rest at a spot in the north church (section 19, 
grave 12) where his second wife had previously been interred 
(1694)°: but in 1739 his daughter Maria erected a monument 

" Cf. p. 314 infra. 

* Weld (1848), Vol. I, p. 245. This also has disappeared. 

* “met 16 d°. en met koetsen en 3 poose luijens’’ (Begrafenisregister 
Oude Kerk. No. 138 Archief Delft). I am indebted to Dr Schierbeek and 
Mevr. Bouricius for this extract. From other entries in the Archives it 
appears that L. was actually entitled to have 18 pall-bearers. 

* This accounts for the different dates of burial given by Schierbeek 
(1930)—31 Aug. and 2 Sept. 1723—as he informs me in a letter. 

° Discovered by Jhr. mr. E. A. van Beresteijn, and communicated to 

Dr Bouricius—from whose posthumous papers the details given above have 
been published by Dr Schierbeek (1930). 


to his memory—on the north side of the tower, in the north 
transept—and the two bodies were then transferred to its foot 
(section 22, graves 14 and 15), where they now he. Maria 
was buried in the same sepulchre* on 30 April 1745. 

The tomb of Leeuwenhoek is shown in Plate XV, which is 
reproduced from an old engraving.” It is little altered at the 
present day.” On the stone pedestal, which rests upon two 
plinths and is surmounted by a white marble skull and 
crossbones flanked by two spheres, is the inscription: 


On the obelisk rising from the pedestal there rests a white 
marble urn supporting a gilt torch; and a circular plaque 
of similar marble, surrounded by decorative ribbon-work, 1s 
affixed to the front. The plaque bears a profile portrait of 
Leeuwenhoek. On the front of the obelisk is inscribed : 



1 This tomb was purchased by L. himself on 8 June 1686 (fide Schierbeek, 
? Supplement to Boitet (1729)—not found in all copies of this work. 

° The only recent description of the tomb is that of Harris (1921), who 
appears to have visited it under unfavourable conditions and was con- 
sequently displeased. But his knowledge of L. was obviously very 
superficial, and his paper—in a popular journal—cannot be taken seriously. 

‘Pp. = posuit. “To her most beloved Father this monument his 
daughter Maria van Leeuwenhoek mourning has erected.” 

> “mo the fond and everlasting memory of Antony van Leeuwenhoek, 
Fellow of the English Royal Society, who, by detecting through diligent 
application and scrutiny the mysteries of Nature and the secrets of natural 
philosophy by means of microscopes invented and marvellously constructed 
by himself, and by describing them in the Dutch dialect, has earned the 




aaa me eo Ol ve tne 

Lafnt At 

Jn fapaya Farad =N Aenea Go ~~ 

0 a a ru wu rm 

See a Fanny ae 8 tm Iam Wn Sea ie I, Toe Mea aT 

{Spinella eben vorlahsfei 



Sea =e w= AWAY, 

oe Fe oe 66 Se wT TD 





wekeer 9 



aera a ou oe tu a Oe oe om 

SF NT TN I a nm 

hina 8 na a an 9a oa 
Sree or SSS 

West Front—viewed from Oude Delft. 
From an engraving by P. Smith after C. Decker, published by Boitet (1729). 

facing p. 100 

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—— 7 

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mage one ane aa 



From an engraving by J. C. Philips (1740) after a drawing by the designer, 
T. Jelgersma. 

facing p. 101 


The monument is set in an arched niche, doubly recessed, 
the pilasters of the inner arch bearing two stone lamps and 
its apex the veiled head of a woman. ‘The whole is protected 
by a decorative’ iron railing. On the floor, in front of the 
railing, is a stone slab covering the tomb. Upon this is cut: 



This is followed by some verses “ to the reader ”’ composed 
by Leeuwenhoek’s young friend and fellow-townsman Hubert 
Poot (1689-1733)—the rustic poet who has been called the 
‘Bobbie Burns of Holland” (see Plate XVI)—which run 






highest approbation of the whole world. Born at Delft 24 October 1632, and 
died in the same place 26 August 1723.”—The final words “de toto . . . 
meruit”’ ave curiously mistranslated “by which he astonished the whole 
world” by Wildeman (1903, p. 48). 

' Morre (1912), following Wildeman (1903), describes this as “elegant ”’: 
but Harris (1921) regards it as particularly nasty. I eall it “ decorative ”’ 
in a descriptive sense: the reader can form his own estimate of its artistic 
merits from the illustration. 

* “Here lieth Anthony van Leewenhoek, oldest Fellow of the Royal 
Society in London, born within the town of Delft on the 24th of October 
1632, and deceased on the 26th of August 1723, being aged 90 years, 10 
months, and 2 days.”’ Note the spelling of L.’s name and the rest of the 
inscription—-which has been “ corrected’ by every previous transcriber. 

* “ Since everyone, O traveller, 
Great age respecteth, everywhere, 
And gifts of wondrous merit : 
So here all reverently tread, 
Where Science old and gray of head 
In LEEWENHOKK lies buried.” 


At the foot of the tombstone has been added an inscrip- 
tion stating that along with her father lies “Maria van 
Leeuwenhoek, his daughter, born at Delft the 22nd of 
September 1656, and passed away the 25th of April 1745.” 
There is also a carved flying eagle, clutching a shield on 
which the coat-of-arms of the Leeuwenhoeks was probably 
once emblazoned.’ 

The following entry’ relating to Leeuwenhoek’s tomb is 
to be found in the Archives of Delft, from which it was 
extracted and published by Soutendam (1875) *: 

In the North Transept of the Old Church of Delft, 
against the wali of the tower, was erected in the year 1739, 
at the expense of Mistress Maria van Leeuwenhoek, in 
memory of her late father the world-famed Mr. Anthony 
van Leeuwenhoek (son of Phillip van Leeuwenhoek, 
Anthony’s son, and of Margaret Bel van den Bergh, 
James’s daughter), under the supervision and care of 
Mr. William van der Lely, at that time Councillor 
and Treasurer of the town of Delft, an Obelisk, simply 
but bravely and elegantly designed by the artist Taco 
Jelgersma, at Haarlem, and wholly wrought by the 
stone-mason Gerrit van der Giesen. 

There is little more to add: but after recording the handi- 
work of Mr Gerard van der Giesen, the good Dutch mason, 
T should like to recall a few lines left by the more sensitive 
hand of an Englishman, Martin Folkes “Esq., Vice-President of 
the Royal Society, in his report on the microscopes bequeathed 
to the Society by Leenwenhoek. Folkes’s account of these 

* See p. 305 infra. 

? IT translate Soutendam’s transcription—not having seen the original. 
It is not unlikely that our famous “ English” artist Sir Peter Lely was a 
kinsman of the Willem van der Lely, sometime Burgomaster of Delft, 
whose signature was appended to this document. 

° I give it in full, because the information supplied by Boitet (1729, 
supplement), Haaxman (1875), Morre (1912), and others, is incomplete. 

* Martin Folkes (1690-1754) was an antiquary, and a distinguished man 
in his day. He studied in France (Saumur) and later at Cambridge. He 
was elected F.R.S. in 1714, Vice-President of the Society in 1723, and 
was President from 1741 to 1753: he was also President of the Society of 
Antiquaries (1750) and a member of the Académie des Sciences (1742)2 Oe 
Dict. Nat. Biogr. and Rec. Roy. Soc. 














essed several panegyric poems 



and addr 

S epitaph, 

Who wrote Leeuwenhoek’ 





1m 1n 


to h 

ao O 
> K 
g 2m 
te) d= 
| (0) 
ty EB 


WM 6 
o FA, 
GS a> ® 
gB 9 
Oo +, 
4 O06 

facing p. 102 







Cir etd 

ps © * 



aca Age 

ee ‘ a rene es msg an | 
. Ph ® | . : | 
ve ee ooh Pann * 
& i 7 if aa A, P ath a é . ive n 
i 7 - 7 x 
ifs A WSs 
aoe 7B) or bp is ; 
, : * 64 ; ; 
. 7 . a + ; ; 
« - » < : 
Tn oe . 
tee Cs , oe LZ i - 
a ang ae 7 
ee ‘ 2. . 
se 7 - 
fas od le ; c . ' ; re 
p Hedi: | 
| i ; ; 1 a a 
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| re TY 9 ak sch 
: , : s } - 
it, ; 4 2 s | . | 
= ie iy i | ; : 
he Bh > | 
‘ mf aes ; a | 

a Ave ay 

oo fa | 

a - - 
ai ¥ es nigh bebe aad Sar on 
en oe eet | raat 


Ui ee te weer A ae 
7 ron " ola tale gn Ses Li | 
alba aA ae Py 




instruments will be considered later ': I shall here give only 
what he says about their maker, because it shows how 
Leeuwenhoek was regarded by the Society at that date and 
will serve as a funeral oration—for want of any other or 
better. In the Philosophical Transactions for November and 
December, 1723, Folkes wrote’: 

It is now above 50 Years, since the late Mr. Leewwenhoek 
first began his Correspondence with the Royal Society ; 
when he was recommended by Dr. Regnerus de Graaf, as 
a Person already considerable by his Microscopical 
Discoveries, made with Glasses contrived by himself, 
and excelling even those of the famous Hustachio Divini, 
so much talk’d of in the learned World: And as he has 
ever since that Time apply’d himself, with the greatest 
Diligence and Success, to the same Sort of Observations, 
no Doubt can be made of the Excellency of those Instru- 
ments he so long us’d, so much improv’d, and upon the 
fullest Experience so often commended in his Letters ; 
great Part of which, at his Decease, he thought fit to 
bequeath to this Society, for whom he ever express’d 
the greatest Esteem and Respect. 

He had, indeed, intimated this Design in several of his 
Letters, and in his last Will and Testament’* gave 
Orders, that the Glasses should be delivered as soon as 
conveniently might be after his Decease; which was 
accordingly done, by the Directions of his surviving 
Daughter, Mrs. Maria Van Leeuwenhoek, to whose great 
Care we are obligd, for the safe and speedy Delivery of 
this very curious and valuable Present.’ 

" See p. 314 sq., infra. * See Folkes (1724). 

* According to Servaas v. Rooijen (1904, p. 384), L.’s will is still extant 
in the protocols of the notary Jan de Vries at Delft. I have not seen this 
document—executed jointly by Antony and Maria, “ both being sound of 
mind and body,” on 30 November 1721. 

* = Mistress: a title applied at that date, of course, to unmarried 

° Here follows an account of the cabinet of microscopes, and a list of 
the objects placed before them. See p. 314 sq., infra. 



It were endless .... to give any Account of Mr. 
Leeuwenhoek's Discoveries ; they are so numerous as to 
make up a considerable Part of the Philosophical Trans- 
actions, and when collected together, to fill four pretty 
large Volumes in Quarto, which have been publish’d by 
him at several Times: And of such Consequence, as to 
have opened entirely new Scenes in some Parts of 
Natural Philosophy, as we are all sensible, in that famous 
Discovery of the Animalcula in Semine Masculino,' which 
has given a perfectly new Turn to the Theory of 
Generation, in almost all the Authors that have since 
wrote upon that Subject. 

But however excellent these Glasses may be jude’d, 
Mr. Leeuwenhoek’s Discoveries are not entirely to be 
imputed to their Goodness only: His own great 
Judgment, and Experience in the Manner of using 
them, together with the continual Application he gave 
to that Business, and the indefatigable Industry with , 
which he contemplated often and long upon the same 
Subject, viewing it under many and different Circum- 
stances, cannot but have enabled him to form better 
Judgments of the Nature of his Objects, and see farther 
into their Constitution, than it can be imagined any 
other Person can do, that neither has the Experience, 
nor has taken the Pains this curious Author had so long 

Nor ought we to forget a Piece of Skill, in which he 
very particularly excell’d, which was that of preparing 
his Objects in the best Manner, to be view’d by the 
Microscope; and of this I am perswaded, any one will be 

* The discovery was announced in a letter written to the Royal Society 
in November 1677—at the very moment when the marriage of William and 
Mary was being celebrated in London. 


Some further particulars of the microscopes themselves follow here: 

ef. p. 317 wnfra. 


satisfied, who shall apply himself to the Examination of 
some of the same Objects as do yet remain before these 
Glasses ; at least, I have my self found so much Difficulty 
in this Particular, as to observe a very sensible Difference 
between the Appearances of the same Object, when 
apply’d by my self, and when prepared by Mr. 
Leeuwenhoek, tho’ view’d with Glasses of the very 
same Goodness. 

I have the rather insisted upon this, as it may be a 
Caution to us, that we do not rashly condemn any of 
this Gentleman’s Observations, tho’ even with his own 
Glasses, we should not immediately be able to verify 
them our selves. We are under very great Disadvantages 
for want of the Experience he had, and he has himself 
put us in Mind, more than once, that those who are the 
best skill’d in the Use of Maenifying-Glasses, may be 
misled, if they give too sudden a Judgment upon what 
they see, or ’till they have been assured from repeated 
Experiments. But we have seen so many, and those of 
his most surprizing Discoveries, so perfectly confirm’d, 
by great Numbers of the most curious and judicious 
Observers, that there can surely be no Reason to distrust 
his Accuracy in those others, which have not yet been so 
frequently or carefully examin’d. 

Upon the whole, it is to be hoped, some of the Society 
will pursue those Enquiries, the late Possessor of these 
Microscopes was so deservedly famous for; and that as 
we have lost in Mr. Leeuwenhoek a most worthy Member, 
and a most valuable Correspondent, this last Piece of his 
Respect to the Royal Society will not only enrich our 

Repository, but both encourage and enable 
some other diligent Observer 
to prosecute the same 
curious and useful 





While ruder heads stand amazed at those 
prodigious pieces of nature, as Elephants, 
Dromidaries, and Camels ; these I confesse, 
are the Colossus and Majestick pieces of 
her hand; but in these narrow Engines 
there is more curious Mathematicks, & 
the civility of these little Citizens, more 
nearly sets forth the wisdome of their 
Maker.—Sir Thomas Browne (1642). 

ae . ey 7 Te F . ; : 
- an y ie a 
ete A) ie th a ; : 

; coe . 




(Letters 6, 13, 13a, 18, 188) 

EEUWENHOEK’S observations on the free-living 
le Protozoa probably began with his discovery of certain 
“very little animalcules”’ which he saw in fresh water 
in the year 1674. He described his findings in a letter 
addressed to Mr. Oldenburg,’ and dated from Delft, 
7 September 1674. This letter deals with other matters also, 
and the passage in which the Protozoa are mentioned is quite 
short. (See Plate XVII.) Here it is, in its entirety °: 

About two hours distant ® from this Town there lies an 
inland lake, called the Berkelse Mere, whose bottom in 

‘ Henry Oldenburg, Secretary of the Royal Society. See p. 38. 

2 Hrom Letter 6. 7 September 1674. MS.Roy.Soc. [Not in Dutch or 
Latin collected works.] Part of this letter was translated and printed in 
Phil. Trans., Vol. 1X, No. 108, pp. 178—182 [misprinted 821], 23 Nov. 
1674. It is numbered “ [10] Brief Tr. 7’ by Vandevelde (1922, p. 344), 
who gives an abstract of it in Flemish (from the Phil. Trans. version—not 
from the MS.). The important passage given above has been generally 
overlooked by protozoologists—possibly because the letter was omitted, 
apparently by an oversight, from the table of contents at the beginning of 
the number in which it was printed. The passage here given begins on 
p. 181; and I have followed the original translation pretty closely, because 
it is so lively and faithful. I havea strong feeling—but no direct evidence— 
that it was not the work of Oldenburg himself: but I do not know who the 
translator was. The English MS. has not been preserved.—I find since 
writing the above that attention was directed to this passage—as fixing the 
date of L.’s earliest observations—by Schill (1887), who reprinted the 
original English version. His note has seemingly been overlooked by all 
later writers. 

® John Ray, in his Journey through the Low-countries, notes (anno 1663) 
as a peculiarity that ‘ they reckon or measure their way in these Countreys, 
by the time they spend in passing it” (Ray, 1673; p. 93). 




many places is very marshy, or boggy. Its water is in 
winter very clear, but at the beginning or in the middle of 
summer it becomes whitish, and there are then little 
green clouds floating through it; which, according to the 
saying of the country folk dwelling thereabout, is caused 
by the dew, which happens to fall at that time, and which 
they call honey-dew. This water is abounding in fish, 
which is very good and savoury. Passing just lately’ 
over this lake, at a time when the wind blew pretty hard, 
and seeing the water as above described, I took up a little 
of it in a glass phial; and examining this water next day, 
I found floating therein divers earthy particles, and some 
green streaks, spirally wound serpent-wise, and orderly 
arranged, alter the manner of the copper or tin worms, 
which distillers use to cool their liquors as they distil 
over. The whole circumference of each of these streaks 
was about the thickness of a hair of one’s head. Other 
particles had but the beginning of the foresaid streak ; 
but all consisted of very small green globules joined 
together: and there were very many small green globules 
as well. Among these there were, besides, very many 
little animalcules,’ whereof some were roundish, while 
others, a bit bigger, consisted of an oval. On these last I 
saw two little legs near the head, and two little fins at 
the hindmost end of the body.* Others were somewhat 
longer than an oval, and these were very slow a-moving, 
and few in number.’ These animalcules had divers 
colours, some being whitish and transparent; others 

nu laest MS. The date of the observation is not more precisely stated, 

but it seems clear that the discoveries must have been made in the late 
summer (end of August or beginning of September ?) of 1674. 

> The common green alga Spirogyra: the earliest recorded observations 
on this organism. ‘The size of the filament negatives the suggestion that L. 
could have been referring to Arthrospira or Spirulina. 

* It can hardly be doubted that some, at least, of these animalcules were 

* Probably Rotifers—seen under a low magnification. 


Probably Ciliates. 


aoe ang Vewr ;LvrewecR Bee apes apr se = 
eer 82d, Wot taset oon) Oy Ee j ow wee eronuk LI Galo} 
Bate! ta Os care Vevee nee “Die Ventvy 6 Sacer ae ee ee 
; L 3 ¥, gR Be i coast Vas eae ay 
’ ig yok Went Iw obs oa 
pes ea phe Aes pees Fae (ere Ceuta 225s) 
Que Bar akdsed. das LET PES ray Tye day Dee oe NA AEG a 

leer ae ae, 

PIT OS bese ak 67 ote wd 9 a9) ent A L/ 
Chane Ss rr ee eae StS treme hy eh ae, 
eee sae. SD BR. Casw Neen ous & Sue ae 
made Le Seth Oem Yosh asd)J ae tll DabLaSY v2, 

Sas Res coger ee ¥ g Sue J ceocotga5, af ye Safes Lense (20: a 
rot «Coot Cul eee: Md , S2S~ Crovase R 0.94.9 on Srbey Book ao Gore. 
ae Creme eee et OF 25, yi greet Cb Se / Otto a 
BS Syrent + adie Casres ick ioe pa ae Ee 
a DG wee a ee 5 B86 Lica dw, LaB9F Apo BLY Sal 
aoe! Qoeent Ca. St) QAeinwKe Slo 
: sth peeved tne; oie ee = 

Gear i freed 3. (Oe ee yA eee $ ee a ee ics J. 
ies a sae rick Sok At ; Cha ae foro SH % eae i wt Loe Gotse Ss 
oy ov Goves ~ > Joe om RE, at ~a om a circle, 
fet Ql oe ao an oon witae als ee AS) a SO hege IR VCnaKe 

ats os A eoynseS VWoetgsns pont eee weet 7 one OS Rods CDI HSS 


(7 Sept. 1674: leaf 3 recto = p. 5), showing the original of the passage here 
translated. Holograph MS. The concluding words are on the verso of the 
page, and read: “.. . int tarwen meel, in schimmel, en etc. heb gesien.” 
Apart from this unavoidable omission, the passage is complete. 

facing p. 110 

i 2H: hse sa pie ' i) 
"a cher ae ee yey oy vn a i mk dw 
He ‘i ne A ‘e 
ND i uate if hy ok ’ 
ene f 

yi ah | 
n oa gh ae) 

AY -” habs 


with green and very glittering little scales; others again 
were green in the middle, and before and behind white’ ; 
others yet were ashen grey. And the motion of most of 
these animalcules in the water was so swift, and so 
various, upwards, downwards, and round about, that ’twas 
wonderful to see: and I judge that some of these little 
creatures were above a thousand times smaller” than the 
smallest ones I, have ever yet seen,’ upon the rind of 
cheese, in wheaten flour, mould, and the like. 

No further observations on these ‘little animals” appear 
to have been reported until more than a year later. But in a 
letter written in December, 1675, Leeuwenhoek again alludes 
to them briefly, in the following words :* 

In the past summer I have made many observations 
upon various waters, and in almost all discovered an 
abundance of very little and odd animalcules, whereof 
some were incredibly small, less even than the animalcules 
which others have discovered in water, and which have 
been called’ by the name of Water-flea, or Water-louse. 

This passage is important as establishing the date when 
some of Leeuwenhoek’s earliest observations were made—the 
summer of 1675. At this time, however, he gave no more 
detailed account of his discoveries: but he kept a careful 
record, and a month later the following passage occurs in a 
further note to Oldenburg :° 

* Probably Euglena viridis. The peculiar arrangement of the chromato- 
phores in this species gives the flagellate this appearance under a low 
magnification. The identification seems to me almost certain; and, if 
correct, this is the first mention of Huglena, whose discovery is usually 
attributed to Harris (1696). 

> i.e., in volume—not in linear dimensions. 

* i.e., mites. 

* From Letter 13. 20 December 1675. MS.Roy.Soc. Unpublished. 
Original in Dutch. 

* By Swammerdam. See note 1 on p. 118. 

° From Letter 13a. 22 January 1676. MS.Roy.Soc. Unpublished. 
Original in Dutch. 



The living creatures discovered by me in water, were 
in ordinary rain-water, that was caught from a pantile 
roof’ in stone troughs under the ground, or in tubs; also 
in well or spring water, coming up through well-sand ; 
likewise in the canal water, that runneth through this 
Town and through the country. Upon these I have 
made divers notes, concerning their colour, figure, the parts 
whereof their body is composed, their motion, and the 
sudden bursting of their whole body; of which notes I 
keep a copy by me, which I shall send you at the earliest 

The promised ‘“ notes”? were sent in due course: they form 
the celebrated letter (Letter 18) which protozoologists have 
long regarded as the first paper ever written upon the objects 
of their special study. Moreover, this letter also contains the 
first account ever written of the Bacteria, as well as many 
other original observations. In view of its unique interest, 
therefore, I must say a few further words of introduction at 
this point. 

Leeuwenhoek’s 18th Letter. 

The famous “ Letter on the Protozoa” is a truly amazing 
document. According to my reckoning it is Leeuwenhoek’s 
eighteenth scientific epistle to the Royal Society, and I shall 
therefore refer to it henceforward simply as Letter 18. The 
original Letter itself is preserved among the Royal Society’s 
manuscripts, and is still—except for a few slight mutilations— 
intact. It is in Dutch, and covers 17} folio pages, closely 
written in a neat small hand which is not Leeuwenhoek’s own, 
though the manuscript has been carefully corrected by him 
throughout (in a different ink), and bears his autograph 
signature at the end. It seems likely that he wrote the letter 
himself, with his notebook before him, and then caused his 

1 The water so collected was probably very clean water: for Dutch 
houses then—as now—were wont to be kept clean both inside and out. 
John Ray, in the diary of his Travels—writing in 1663—notes that, in the 
Netherlands, ‘‘all things both within and without” were “ marvellously 
clean, bright, and handsomly kept: nay some are so extraordinarily curious 
as to take down the very Tiles of their Pent-houses and cleanse them.” 
Vide Ray (1673), p. 52. 

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( $2r.) 

Obfervations communicated to the Publier by Mr. Antony van 
Leewenhoeck, én 4 Dutch Letter of the 9th of O&ob. 1676, 
here Englify’d: Concerning little Animals by hire obferved in 
Rain- Welle Sea- and Snow-water ; as alfo in water wherein 
Pepper hadlain infufed. 

N the year 1675.1 difcover’d living creatures in Ra'n water, 
which had ftood but few days in anew earthen pot, glafed 
blew within, This invited me to view this water with great at- 
cention,efpecially thofe little animals appearing to me cen thou- 
fand times lefs than thofe reprefented by Monf. Swamerdam, 
and by him called Water-fleas or Water-dice, which may be per- 

ceived in the water with the naked eye, 3 
The fir fore by me difcover’d in the faid water, I divers 

times obferved to confit of 5, 6,7, or 8 clear globuis, without 

being able to difcern any film that held them together, or con- 
tained them. When thefe amimaicula or living Atoms did move, 
they put forth two little horns,continually moving themfelves: 

The place between thefe two horns was flat, though the reft of 

the body was roundifh,fharpning a little towards che end,where 

they hada tayl, near four timesithe length of the whole body,of 
the thicknefs (by my Microfcope) ofa Spiders-web ; at the end 
of which appear’d a globul, of the bignefs of one of thofe which 
made up the body; which tayi I could not perceive,even in ve- 
ry clear water, to be mov’d by them. Thefe little creatures, if 
they chanced to light upon the leait filament or ftring,or other 
fuch particle, of which there are many in water,ef{pecially after 
it hath ftood fome days, they {tock intangled cherein,extending 
their body ina long round, and ftriving to dif-intangle their 
tay] ; whereby it came to pafs, that their whole body lept back 
towards the globul of the tay], which then rolled together Ser- 
pent-like, and after the manner of Copper- or Iron-wire that 
having been wound abouta ftick, and unwound again, retains 
thofe windings and turnings. This motion of extenfion and 
contraétion continued a while; and I have feen feveral hun- 
dreds of thefe poor little creatures, within the fpace of a grain 
of profs fand, lye faft clufter’d together ina few filaments. 
Lalfo difcover’d a fecond fort, the figure of which was ova! ; 
and I imagined their head to ftand on the tharp end.Thefe were 

a little bigger than the former. The inferior part of their body 

is flat, furnifhed with divers incredibly thin feet, which pyar 


(9 Oct. 1676) published in Phil. Trans. (1677), Vol. XII, No. 183, 

pp. 821-831. Compare with Plate XIX. 
facing p. 1138 


rough draft to be copied out in a fair hand before sending it to 
the Society. The letter is dated from ‘ Delft in Holland, 9th 
October, 1676”’ [New Style], and is addressed to Henry 
Oldenburg in person. From an endorsement which it bears’ 
it appears that he received it 10 days later, and sent back an 
acknowledgement of its receipt through Leibniz. The letter 
was read at the meetings of the Royal Society held on 1, 16, 
and 22 February 1677 [O.S. ].’ 

A part of this letter was published (in English) in the 
Philosophical Transactions in March, 1677,’ under the heading 
“ Observations, communicated to the Publisher * by Mr. Antony 
van Leewenhoeck, in a Dutch Letter of the 9th of Octob. 1676. 
here English’d: Concerning little Animals by him observed in 
Rain- Well- Sea- and Snow-water; as also in water wherein 
Pepper had lain infused”. (See Plate XVIII.) This English 
version was the work of Oldenburg himself, as is evident from 
the manuscript translation—in his hand—still preserved with 
its Dutch original. 

Oldenburg’s English rendering is the only version of 
Letter 18 which has hitherto been printed. It is, on the 
whole, good: but it is not perfect, and most people will be 
surprised to learn that it is a condensed translation of less 
than half of the original, and that the part which Oldenburg 
did not print has never yet been published in any language. 
Why the letter has never been published, in its entirety, I do 
not know. I can only suppose that no protozoologist or 
bacteriologist has ever yet seen the original manuscript; or, 
having seen it, has had the courage and diligence to decipher 

1 The endorsement—in Oldenburg’s hand—is as follows: “recew le 9. 
Octob. st. v. [=style vieux] 1676. resp[ondu]. le 16 Oct. d’avoir receu 
cette lettre, par M. Leibnitz, mais non pas encor consideré”’.—It was in the 
autumn of 1676 that Leibniz paid his now well-known (but formerly hushed- 
up) visit to Spinoza at The Hague (cf. Pollock, 1899; p. 37). Perhaps 
Oldenburg, knowing this interview to be imminent, requested Leibniz to send 
word to L.—only a few miles distant at Delft—of the safe receipt of his 
letter. I can find no evidence to show that Leibniz visited Leeuwenhoek 
on this occasion.—The well-known correspondence between L. and Leibniz 
took place, of course, at a much later date, and has been already reviewed 
by Ehrenberg (1845). 

2 Cf. Birch, Vol. III, pp. 332, 333, 334. 
* Phil. Trans. (1677), Vol. XII, No. 133, pp. 821-831. 
* “Publisher”? = Editor (¢.e. Oldenburg). 



it. It certainly is not very easy to read; but considering its 
supreme interest and importance, I am astonished that nobody 
hitherto appears to have made the attempt—nobody, that is, 
since Oldenburg: for Oldenburg evidently read the whole 
letter, and, though he published but a part, translated most 
of it—after a fashion. I have been through his manuscript 
translation carefully, but I have made no use of it in the 
preparation of my own: for it is much too abbreviated and 
confused for my purpose, and it is not free from errors. 
Oldenburg seems to have had a fair knowledge of Dutch, but 
the objects which Leeuwenhoek was endeavouring to describe 
were, of course, at that time entirely outside the experience 
of everybody but himself: and to understand his words, and 
to appreciate his efforts at description, it is necessary to be 
familiar with the things that he was studying as well as with 
his way of writing. 

Many protozoologists have, no doubt, read Oldenburg’s 
curtailed English version of Letter 18 in the Philosophical 
Transactions, but probably many more are acquainted with it 
through the work of Saville Kent. This author copied a 
considerable part of the letter into his well-known book on 
the ‘“ Infusoria’”’!; but I must remark that his quotations from 
Oldenburg’s translation do not altogether bear out his own 
statement that they were transcribed “with a faithful 
reproduction of their original quaint style of diction”. Kent's 
version is, indeed, by no means faithful to its prototype, and 
even contains several bad mistakes. For example, in one 
place Leeuwenhoek says that he put some water in a glass 
“on mijn comptoir’’—meaning “in my closet,” z.e. the office 
or study”? in which he worked and wrote (probably the 
counting-house in his shop). This frequently recurring phrase 
is usually rendered ‘“‘in musaeo meo”’ by the Latin translators, 
and appears—concordantly —as “dans mon cabinet” in the 

* Manual of the Infusoria (1880). Vol. I, pp. 3-7.—I may also note 
here that what purports to be another reproduction of the same letter, 
published recently by Knickerbocker (1927), is nothing more than a reprint 
of the garbled and condensed version printed in 1809 by Hutton, Shaw, 
and Pearson in their Abridgement of the Phil. Trans. It has no value either 
as a historical document or as an illustration of L.’s work. 

* Comptoir = reekenkamer, schrijfkamer, etc. (Meijer, Woordenschat p. 56). 
spe particulars regarding L.’s “ comptoir ” are given in Letter 16 (p. 125 


short French version of Chr. Huygens.’ Oldenburg rightly 
translated it ‘in my Counter’ or Study ’’—evidently being at 
a loss for the exact English equivalent of the Franco-Dutch 
word. But Kent, by “copying” Oldenburg, ultimately gives 
us “on my counter of study’’—an unintelligible expression 
which he perhaps imagined to mean “on my laboratory 
bench ”’.* 

On 7 November 1676, a month after he had sent his long 
letter to the Royal Society, Leeuwenhoek wrote a much 
shorter account of the same observations to his old friend 
Sir Constantijn Huygens—the statesman-poet father of 
Christiaan, the famous astronomer and mathematician. This 
letter *is preserved at Leyden, and has recently been published 
by Vandevelde and van Seters (1925). At Leeuwenhoek’s 
request it was translated into French by Christiaan Huygens 
—then at Paris—whose MS. translation is also now in the 
Leyden University Library along with its Dutch original. 
This French version was evidently intended for presentation 
to the Paris Academy: but another French abstract or 
summary of Leeuwenhoek’s observations was printed in the 
Journal des Scavans some two years later,’ and the translation 
made by Huygens has only recently been published in 
Holland.° These various abstracts give but a poor idea of 

™ See note 6 below. 

> i.e. Counting-house (reekenkamer). 

° I regret to say that at least one modern Dutch translator and one 
Flemish commentator have fallen into the same error. They should both 
have known better. 

* Letter 18b, according to my numeration. Referred to by Haaxman 
(1875), p.135. Snelleman (1874) has printed a part of this letter, in the 
original Dutch, but his version contains several manifest misreadings which 
Vandevelde and van Seters have rectified. I have carefully compared the 
(published) letter of 7 Nov. 1676 with Letter 18, and it is obvious that it is 
merely a very condensed account (not half the length) of the latter. It 
contains nothing that is not more fully given in the original (Letter 18, 
9 Oct. 1676) addressed to the Royal Society. The comparison instituted by 
Vandevelde and van Seters between the French and Dutch abstracts and 
Oldenburg’s short English version seems somewhat unprofitable, since they 
never consulted the Dutch original in extenso (Letter 18). 

> Journ. d. Scav., Vol. IX. 1678 (pp. 55 and 68 of nouv. éd., 1724). 

° Gwores Completes de Chr. Huygens (1899), Vol. VIII, pp. 22-27 
(No. 2100). 


the extensive investigations described in the original Dutch 
epistle (Letter 18). 

The greater part of this very long letter—one of the 
longest Leeuwenhoek ever wrote—is in an unusual form. At 
the very end of it he remarks that “these my observations” 
are “ taken from the diary which I keep from time to time;” 
and accordingly we find that he generally gives, in order, the 
observations as he made them from day to day—without 
making any attempt to summarize or correlate them. In his 
letter to Constantijn Huygens (7 Nov. 1676) he explains that 
he sent these details from his notebook “ merely so as to make 
my observations more credible in England and elsewhere; and 
especially because Mr Secretary Oldenburg had formerly 
written to me that there are a number of philosophers at Paris 
and elsewhere who don’t allow of the truth of what I 
describe”*. The subject-matter falls naturally, as will be 
seen, into various sections, dealing with the divers creatures 
found in the several sorts of water or infusions which he 
examined. Some of these sections are provided, by himself, 
with appropriate headings, while others are not: and I have 
therefore, for the sake of uniformity, interpolated such 
headings where they are lacking in the original.’ 

Leeuwenhoek’s 18th Letter opens (cf. Plate XIX) with a 
few personal remarks, of no particular interest in the present 
connexion, and then drops abruptly into the description of his 
discoveries: and at this point I have begun my translation, 
which now follows.* 

* Another French translation (or a copy of one of the two mentioned 
above ?) was published later in a work called Collection Académique de Dijon, 
Vol. II, pp. 454-461, 1755: but this I have not been able to consult. Cf. 
Konarski (1895, p. 251 note) and Vandevelde (1922, p.349)—No account of 
these observations appears to have been published in the Acta Hruditorum, 
which only began publication in 1682: but a reference to L., and the 
discovery of animalcules in infusions (attributed ambiguously to Butterfield), 
will be found in the note by Elsholz (1679) in Miscellanea Curiosa, Vol. IX. 

* See Vandevelde and van Seters (1925), p.20: and Guvres Compl. de 
Chr. Huygens (1899), Vol. VIII, p. 22, footnote 3. 

* These additions, wherever they occur, are indicated by being inclosed 
between square brackets. 

* Letter 18. 9 October 1676. To Oldenburg. MS. Roy. Soc. I have 
not thought it necessary to mark all the places where my translation differs 

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[1st Observation on Rain-water. | 

In the year 1675, about half-way through September ' 
(being busy with studying air, when I had much compressed 
it by means of water”), I discovered living creatures 
in rain, which had stood but a few days® in a new tub, 
that was painted blue within.* This observation provoked 
me to investigate this water more narrowly; and especially 
because these little animals were, to my eye, more than 
ten thousand times smaller’ than the animalcule which 
Swammerdam ° has portrayed, and called by the name of 

from Oldenburg’s, nor yet to point out all his many minor omissions. 
These will be manifest to anybody who will take the trouble to compare 
this rendering with that in the Phil. Trans. Only important errors, 
interesting variants, or vital omissions, are indicated in my notes.— 
Vandevelde (1922, p. 348) numbers this letter ‘ [15] Brief Tr. 11,” but it 
certainly cannot be called ‘‘ Letter 11” or 15” in any sense.—The letter 
is not to be found, of course, in either the Dutch or the Latin edition of the 
collective works. 

* In den gare 1675 ontrent half September MS. “In the year 1675” 
Phil. Trans. By neglecting to translate the latter part of the original 
statement, Oldenburg left the precise date of the discovery in doubt; and 
a controversy arose later between Ehrenberg and Haaxman in consequence— 
the former alleging that the observations were made in April, while the 
latter, on evidence furnished by the MS. letter from L. to Const. Huygens, 
believed the correct date to be mid-September. Cf. Haaxman (1875). It 
is now obvious that Haaxman was right. 

> Some account of L.’s experiments “on the compression of the air” 
had already appeared in Phil. Trans. (1673), Vol. IX, p. 21. (Letter 2, 
15 August 1673. MS. Roy.Soc.) 

* “four days”’ Saville Kent (Vol. I, p. 3). This is merely due to careless 
copying, and is not in the originals. 

. . . . be 
* in een nieuwe ton, die van binnen blaww geverft was MS. in a new 

earthen pot, glased blew within’ Phil. Trans. Oldenburg here mis- 
translated L.’s words, which were quite plain and were rendered concordantly 
by Chr. Huygens “dans un tonneau peint en huile par dedans’”’. The vessel 
was obviously not of Delft porcelain. 

° ¢.e., in bulk—not in diameter. This expression means, with L., that 
he judged the animalcules to have roughly one twenty-fifth of the diameter 
of the bigger creatures. 

® Jan Swammerdam (1637—1680). For his life see especially his 
Biblia Naturae (1737) and Sinia (1878). 


Water-flea, or Water-louse,’ which you can see alive and 
moving in water with the bare eye. 

Of the first sort that I discovered in the said water, I 
saw, after divers observations, that the bodies consisted 
of 5, 6, 7, or 8 very clear globules, but without being able 
to discern any membrane or skin that held these globules 
together, or in which they were inclosed. When these 
animalcules bestirred ’emselves, they sometimes stuck 
out two little horns,’ which were continually moved, after 
the fashion of a horse’s ears. The part between these 
little horns was flat, their body else being roundish, save 
only that it ran somewhat to a point at the hind end; at 
which pointed end it had a tail, near four times as long 
as the whole body, and looking as thick, when viewed 
through my microscope, as a spider’s web.* At the end 
of this tail there was a pellet, of the bigness of one of the 
globules of the body; and this tail I could not perceive 
to be used by them for their movements in very clear 
water. These little animals were the most wretched 
creatures that I have ever seen; for when, with the 
pellet, they did but hit on any particles or little filaments ° 
(of which there are many in water, especially if it hath 

* Swammerdam’s “ watervlooy’”’ was Daphnia—as all students of the 
Biblia Naturae are well aware (cf. B.N. Vol. I, p. 86, Pl. XX XI). But as this 
work was not published until 1737—long after his death—it is clear that 
L. here alludes to his earlier Dutch publication (Swammerdam, 1669), in 
which the water-flea is shown on Pl. I. Swammerdam himself called it 
“the branched water-flea”’, and attributed the name ‘‘ water-louse’’ to 

> Vorticella sp. The following admirable description makes the 
identification certain. 

* The optical section of the wreath of cilia round the peristome—so 
interpreted by most of the early observers. 

* i.e., as thick as a spider’s web looks to the naked eye. 


> maer quamen aen eenige deeltgens of veseltgens MS. ° if they chanced 
to light upon the least filament or string, or other such particle’? Phil. 
Trans. These words of Oldenburg are amusingly mistranslated by Nagler 
(1918, p. 7) ““ Wenn man diese kleinen Kreaturen Zufallig belichtete.” (He 
apparently supposes that “ to light upon’”’ means “‘ to illuminate ” ! ) 


but stood some days), they stuck intangled in them; and 
then pulled their body out into an oval, and did struggle, 
by strongly stretching themselves, to get their tail loose ; 
whereby their whole body then sprang back towards the 
pellet of the tail, and their tails then coiled up serpent- 
wise, after the fashion of a copper or iron wire that, 
having been wound close about a round stick, and then 
taken off, kept all its windings.’ This motion, of stretch- 
ing out and pulling together the tail, continued; and I 
have seen several hundred animalcules, caught fast by 
one another in a few filaments, lying within the compass 
of a coarse grain of sand.” 

I also discovered a second sort* of animalcules, whose 
figure was an oval; and I imagined that their head was 
placed at the pointed end. These were a little bit bigger 
than the animalcules first mentioned. ‘Their belly is flat, 
provided with divers incredibly thin little feet, or little 
legs,* which were moved very nimbly, and which I was 
able to discover only after sundry great efforts, and where- 
with they brought off incredibly quick motions. The 
upper part of their body was round, and furnished inside 
with 8, 10, or 12 globules: otherwise these animalcules 

* Apparently it never occurred to L., at this time, that the contraction 
and extension of the stalk (“tail’’) of Vorticella could have any other 
significance than that here attributed to them. The idea of a stalked and 
normally sessile animal probably never entered his head; and consequently 
he jumped to the incorrect conclusion that the animals were endeavouring 
to “ get their tails loose ’’—which, of course, was a mistake, though a very 
natural one. lL. published pictures of Vorticellids later, in Phil. Trans., 
Vol. XXIII (Letter dated 25 Dec. 1702): and still later he arrived at a 
more correct interpretation of the function of the “tail,” and of the 
organization of these remarkable animals (Send-brief VII, dated 28 June 
1713). See Chapter 4, below. 

* inde spatie van een grof sant MS. “ within the space of a grain of gross 
sand” Phil. Trans. This is a very common expression with L., and 
Oldenburg fully understood its meaning ; but Nagler (1918, p. 9) mistranslates 
his words “in der Héhlung eines grossen Sandkorns’’—as though L. had seen 
the animalcules lying in a cavity in an actual grain of sand! 

* Not identifiable with certainty, but undoubtedly a ciliate. 

y Ve ey: 
2.e. cilia. 



were very clear. These little animals would change their 
body into a perfect round, but mostly when they came to 
lie high and dry. Their body was also very yielding: for 
if they so much as brushed against a tiny filament, their 
body bent in, which bend also presently sprang out again ; 
just as if you stuck your finger into a bladder full of 
water, and then, on removing the finger, the inpitting 
went away. Yet the greatest marvel was when I brought 
any of the animalcules on a dry place, for I then saw 
them change themselves at last into a round, and then the 
upper part of the body rose up pyramid-like, with a point 
jutting out in the middle; and after having thus lain 
moving with their feet for a little while, they burst 
asunder, and the globules and a watery humour flowed 
away on all sides, without my being able to discern even 
the least sign of any skin wherein these globules and the 
liquid had, to all appearance, been inclosed ; and at such 
times I could discern more globules than when they were 
alive. This bursting asunder I figure to myself to happen 
thus: imagine, for example, that you have a sheep’s 
bladder filled with shot, peas, and water; then, if you 
were to dash it apieces on the ground, the shot, peas, and 
water would scatter themselves all over the place.’ 

Furthermore, I discovered a third sort’ of little 
animals, that were about twice as long as broad, and to 
my eye quite eight times smaller* than the animalcules 
first mentioned: and I imagined, although they were so 
small, that I could yet make out their little legs, or little 
fins. Their motion was very quick, both roundabout and 
in a straight line. 

ee ee 

* The foregoing graphic account of the bursting of the “ little animals” is 
of great interest, as it shows clearly that L. was really observing protozoa. 
An animal whose body consisted entirely of soft ‘‘ protoplasm ”—without any 
skeletal parts or obvious skin—was, of course, a considerable novelty at this 



Not identifiable. Probably a small ciliate. 

* «.e., having a diameter equal to about half that of the Vorticella. 


The fourth sort! of animalcules, which I also saw 
a-moving, were so small, that for my part I can’t assign 
any figure to em. These little animals were more than 
a thousand times less than the eye of a full-grown 
louse? (for I judge the diameter of the louse’s eye to be 
more than ten times as long as that of the said creature), 
and they surpassed in quickness the animalcules already 
spoken of. I have divers times seen them standing still, 
as ’twere, in one spot, and twirling themselves round 
with a swiftness such as you see in a whip-top a-spinning 
before your eye*; and then again they had a circular 
motion, the circumference whereof was no bigger than 
that of a small sand-grain; and anon they would go 
straight ahead, or their course would be crooked." 

Furthermore, I also discovered sundry other sorts of 
little animals; but these were very big, some as large as 
the little mites on the rind of cheese, others bigger and 
very monstrous.’ But I intend not to specify them ; and 

1 Probably—from the ensuing description—a species of Monas. Certainly 
not bacteria of any kind. 

2 This makes the diameter of the protozoon here described about 6-8 p, 
and is agreeable with its interpretation as Monas vulgaris. 

? If the description applies to Monas—as I strongly suspect—then the 
“spinning” here described was an illusion. I fancy L. saw a Monas attached 
by its caudal filament, and mistook the swirl of the water at its anterior 
end (occasioned by the movements of the small accessory flagellum) for a 
motion caused by the rotation of the body as a whole. 

4 on dan weder soo regt wijt, als crom gebogen MS. These words are hard 
to understand. The above seems to me to be L.’s meaning : but Oldenburg 
translates ‘and then extending themselves streight forward, and by and by 
lying in a bending posture ”’ (Phil. Trans.). It is hardly likely that L. could 
have observed “a bending posture”’ in an organism so small that he could 
discern “ no figure” in it: and as the “circular motion” just mentioned 
evidently refers to the orbit described by the organism—not to the 
animalcule itself—I imagine that ‘‘regt wijt’” and “‘ crom gebogen” likewise 
refer to the path traversed. I should point out, however, that L. elsewhere 
(Letter 38) applies precisely the same words to the shape of the spermatozoa 
of a frog. 

® Some of these were doubtless protozoa, but the “ monsters’ were 
perhaps rotifers. Much later, when describing these animals, L. mentions 
that he had previously discovered them in rain-water, in which he had 
steeped pepper and ginger. See Letter 144, 9 Feb. 1702. 


will only say, that they were for the most part made up 
of such soft parts, that they burst asunder whenever the 
water happened to run off them. 

The 2nd Observation. [Rain-water.] 

The 26th of May,’ it rained very hard. The rain 
abating somewhat, I took a clean glass and got 
rain-water, that came off a slate roof, fetched me in it, 
after the glass had first been swilled out two or three 
times with the rain-water. I then examined it, and 
therein discovered some few very little animals’; and 
seeing them, I bethought me whether they might not 
have been bred in the leaden gutters, in any water that 
might erstwhile have been standing in them. 

The 3rd Observation. Rain-water. 

On the same date, the rain continuing nearly the 
whole day, I took a big porcelain dish, and put it in 
my court-yard, in the open air, upon a wooden tub 
about a foot and a half high: considering that thus no 
earthy particles would be splashed into the said dish by 
the falling of the rain at that spot. With the water 
first caught, I swilled out the dish, and the glass in 
which I meant to preserve the water, and then flung this 
water away: then, collecting water anew in the same 
dish, I kept it; but upon examining it, I could discover 
therein no living creatures, but merely a lot of irregular 
earthy particles. 

The 30th of May, after I had, since the 26th, observed 
this water every day, twice or thrice daily, I now first 
discovered some (though very few) exceeding little 
animalcules,* which were very clear. 

* Anno 1676. 

* Unidentifiable. The animalcules from L.’s gutters were described by 
himself later. (Cf. p. 263 infra.) They include flagellates, ciliates, bacteria, 
and rotifers. 

* From the description which follows, these were probably the same 
as the “ very little animalcules”’ already described—.e., a species of Monas. 


On the 31st ditto, I discovered more little animals in 
the water, as well as a few that were a bit bigger; and I 
imagine that ten hundred thousand of these very little 
animalcules are not so big as an ordinary sand-grain.’ 
Comparing these animalcules with the little mites in cheese 
(which you can see a-moving with the bare eye), I would 
put the proportion thus: As the size of a’small animalcule 
in the water is to that of a mite, so is the size of a honey- 
bee to that of a horse; for the circumference of one of 
these same little animalcules is not so great as the thick- 
ness of a hair on a mite. 

The 4th Observation. Rain-water. 

On June 9th,’ collected rain-water betimes in a dish, as 
aforesaid, and put it at about 8 o’clock in the morning in 
a clean wine-glass, and exposed it to the air at about the 
height of the third storey of my house, wondering whether 
the little animals would appear sooner in water thus 
standing in the air. 

The 10th ditto, observing this water, I fancied that I 
discovered living creatures; but because they were so 
few, and not so plainly discernible, I could not accept 
this for the truth. 

On the 11th ditto, seeing this water, with the naked 
eye, stirred in the glass by a stiff gale of wind (which had 
now blown from the same quarter for 36 hours; the 
weather being so cold withal, that it did not irk me to 
wear my winter clothes), I had no thought of finding any 
living creatures in it; but upon examining it, I saw with 
wonder quite 1000 living creatures in one drop of water. 

‘This means that he estimated their diameter at something less than 
zdo of the diameter of an “ordinary” (or large) sand-grain. Taking this 
as 35 of an inch, their diameter would thus be of the order of so00 in., or 
roughly 8°5. This is a very close guess at the size of Monas vulgaris. On 
sand-grains cf. p. 334 fra. 

? Anno 1676. 


These animalcules were of the smallest sort’ that I had 
as yet seen. 

The 12th of June, in the morning (the wind being west, 
with both sunshine and an overcast sky), observing again, 
I saw the foresaid animalcules in such great numbers in 
the water which I took from the surface, that now they 
did not amount to merely one or two thousand in one 

The 13th ditto, in the morning, examining the water 
again, I discovered, besides the foresaid animalcules, a 
sort of little animals that were fully eight times as big’ 
as the first; and whereas the small animalcules swam 
gently among one another, and moved after the fashion 
of gnats in the air, these large animalcules had a much 
swifter motion; and as they turned and tumbled all 
around and about, they would make a quick dart.°® 
These animalcules were almost round. * 

On the 14th of June I did perceive the very little 
animalcules in no less number. 

On the 16th ditto, the animalcules seen as before; and 
the water (which had been, in all, about 4 of a pint) 
being now more than half dried up, I flung it away. 

5th Observation. Rain-water. 

The 9th of June,’ I put some of the last-collected 
water, likewise in a clean wine-glass, in my closet; and 

*4.e., probably Monas sp. again. 
? On L.’s system this means “ twice as long”. 

= nmamen deselve een snelle scheut MS. “and then making a sudden 
downfall”? Phil. Trans. L.’s meaning seems clearly to be that given above 
(i.e., they sometimes made sudden shoots or darts forward). Oldenburg 
renders his words as though scheut = Fr. chute. 

4 It seems to me almost certain that the animalcule here described was 
the common ciliate Cyclidiwm. This is the only likely organism—of this 
order of magnitude—which makes sudden springs (hence its name of “ flea- 
animalcule”’). The only objection to this interpretation is the statement 
that it was ‘‘almost round’’: but it must be remembered that L. made 
his observations under a very inadequate magnification. 

> Anno 1676. 

iat int ‘ag FY eo 
ay Oi 

by set) Gains 





From the picture by Jan Vermeer (1632-1675). This three-storey house is 
probably very like the one in which Leeuwenhoek lived. The picture shows 
the casement windows, with their leaded panes and wooden shutters, and 
an alleyway leading to the yard at the back (where the well was situated) : 

only the canal in front of the house is not shown below the cobbled 
pavement in the foreground. 

facing p. 125 


on examining it, I descried no animalcules. (Note. My 
closet standeth towards the north-east,’ and is parti- 
tioned off from my antechamber with pine-wood, very 
close joined, having no other opening than a slit an inch 
and a half high and 8 inches long, through which the 
wooden spring of my lathe passeth. ‘Tis furnished 
towards the street with four windows, whereof the two 
lowermost can be opened from within, and which by 
night are closed outside with two wooden shutters; so 
that little or no air comes in from without, unless it 
chance that in making my observations I use a candle, 
when I draw up one casement a little, lest the candle 
inconvenience me; and I also then pull a curtain almost: 
right across the panes.) 

The 10th of June, observing this foresaid rain-water, 
which had now stood about 24 hours in my closet, I 
perceived some few very little living creatures,’ to which, 
because of their littleness, no figure can be ascribed; and 
among others, I discovered a little animal that was a bit 
bigger, and that I could perceive to be oval.* (Note. 
When I say that I have observed the water, I mean I 
have examined no more than 3, 4, or 5 drops thereof, 
which I also then throw away; and in narrowly 
scrutinizing 3 or 4 drops I may do such a deal of work, 
that I put myself into a sweat.) 

' From the situation of the house, this indicates that the “ closet”? was 
at the front, looking on to the canal in the Hippolytusbuurt.—Plate XX is 
inserted here to show the sort of house which L. probably lived in, and to 
illustrate what he means by fowr windows with two wooden shutters over 
the lowermost. (This picture may conceivably have been painted from L.’s 
own house—or Vermeer’s!) Although the original painting (formerly in 
the Six Collection, now in the Rijksmuseum) is now known as Het Straatje 
(= The Little Street), it appears to have been more correctly described as 
“A View of a House in Delft” in the catalogue of the sale of Vermeer’s 
pictures at Amsterdam in 1696. 

* Probably Monas (or Cercomonas): see below. 

* From the observations recorded later, it appears probable that the 
organism was a ciliate; but its very small size is against this interpretation. 
It may have been a Cyclidiwm. 



The 11th ditto, observing this water again, I saw the 
foresaid small animalcules, though very few in number. 

The 12th ditto, I saw the very small animalcules, as 
yesterday ; and besides these, a little animal’ that had 
nearly the figure of a mussel-shell, lying with its hollow 
side downwards. “T'was of a length anigh that of a 
louse’s eye.” 

The 13th ditto, in the morning, I found the said very 
small animalcules in greater number, and I saw also one 
bigger animalcule, like that just spoken of.” The same 
day, in the evening, I perceived the said very small 
animalcules again in no less number; and I could now 
see that they had a clear or transparent projection at the 
hind end of their body.* Moreover I discovered animal- 
cules which were somewhat longer than an oval.’ These 
were about 6 times as long as the foresaid very small 
animalcules ; and their head, which was somewhat long 
drawn out, they oft-times pulled in, and then looked to 
be almost round. ‘There were also animalcules’ which 
appeared perfectly round, their diameter being twice as 
long as that of the smallest animalcules of all. These 
two large sorts were very yielding, so that their body did 
bend before the least little filament which they chanced 
to brush against in the water. 

The 14th ditto, I perceived the oval animalcules in 
greater number.’ 

' Traditionally—and doubtless with justice—identifiable as Stylonychia 
mytilus (O.F.M.) Ehrbg., a common hypotrichous ciliate. 

* That is, about 70m. See p. 336. 
*ie., Stylonychia. 

* Probably Monas again—or perhaps a Cercomonas. 

® From the description which follows it seems probable that these were 
Dileptus sp., but it is impossible to identify them with certainty. 

© Perhaps Cyclidiwm again — similarly described on June 13 (4th 

7This apparently refers to the oval animalcules seen on the 10th 
(2 Cyclidiwm). 


The 16th ditto, I perceived the oval animalcules in yet 
greater numbers; and they were flat beneath, and round 
above: and besides these, there were very small animal- 
cules that were three times as long as broad,’ together 
with divers other sorts which it would take all too long 
to specify. In the evening of the same day, I discovered 
little paws on the foresaid oval animalcules,’ which were 
many in number, in proportion to the animalcule; and 
also a much bigger animalcule* of the same figure, that 
was likewise furnished with little legs. And at this point, 
I stopped my observations upon this water. 

6th Observation anent Rain-water. 

On the 17th ditto, it rained very hard in the forenoon, 
and I collected water, as before related, in a new Delft 
porcelain dish, which had never been used before; but I 
found therein no living creatures, only many earthy 
particles, and, among others, bits which I imagined came 
from the smoke of coals’; and some very thin threads, at 
least ten times thinner than the thread of a silk-worm. 
They seemed to be made up of globules; and when they 
lay rather thick one upon another, they had a green 

The 26th ditto, having been eight days out of town 
on holiday, and my closet having stood tight shut up; 
being come home, and observing the water afresh, I 
discovered divers animalcules, which were very small.° 

* Unidentifiable, as no further details are given. Possibly Bodo 

” 2? Cyclidium. The “paws” were obviously cilia. 
* A ciliate; but not determinable, as this is all that is ever said about it. 

* June, 1676. 
° wande rook van smits coolen MS. “from the smoak of Smiths-coals” 
Phil. Trans. “ Smits coolen”’? means ordinary (or stone) coal, as dis- 

tinguished from “ howts coolen’’, or charcoal. The “globules” present in 
smoke are described by L. elsewhere. 

° Unidentifiable. It is not clear from his words whether L. here refers 
to the ‘‘ very small animalcules’”’ (Monas?) previously mentioned or not. 


Thereupon I put my observations upon rain-water on one 
side for the time being. 

[ Observations on River-water. | 

This town of Delft is very well off for water, and in 
summer we get fresh water into the town with all the 
floods seaward from the river Maas; wherefore the water 
within the town is very good, and river fish are caught 
every day by children with fishing-rods in the water- 
ways inside the town. This water being divers times 
examined by me, I discovered in it some exceeding small 
animalcules (so small, indeed, that I could scarce discern 
their figure) of sundry sorts and colours, and therewithal 
some that were much bigger; though were I to specify 
the motion and the make of every one of ’em, ’twould 
take all too long a-writing. But all these animalcules are 
very scanty in this water, compared with those that I saw 
in the rain-water; for if I discovered 25 animalcules in 
one drop of it, that was quite a lot.’ 

[Observations on Well-water.] 

I have in my yard,’ standing in the open air, a well, 
which is about 15-foot deep before you come to the 
water. It standeth at the south, but so encompassed 
with high walls, that even when the sun is in the sign of 
Cancer, the coping of the well is not shone upon. This 
water cometh out of the ground, which is well-sand, with 
such force, that whenever I have tried to empty the well 
there was always about a foot of water still leftin. On 
a summer’s day this water is so cold that ’tis not feasible 
to keep your hand in it for long. Having no thought 
that there would be living creatures in it (for ’tis very 

1 No identification of these “animalcules”’ can be attempted, though 
they must have been protozoa or bacteria. As some of them were coloured, 
it may be inferred that they included Phytoflagellates. 

> op mijn plaets MS. “In the open Court of my house’? Oldenburg 
dans ma cour Huygens. 




as it appeared in Leeuwenhoek’s time. 

National Gallery 

facing p. 129 

by Jacob van Ruisdael (1628 ?- 1682). 





After the o 


palatable and clear), I examined it in September of last 
year, and discovered therein a great number of very 
small animalcules, which were very clear, and a bit bigger 
than the very smallest animalcules that I’ve ever seen. 
And I imagine (having aforetime weighed a grain of 
water), that there were commonly more than 500 living 
creatures in one grain of this water. ‘These animalcules 
were very sedate, moving without any jerks.” 

In the winter’ I perceived no little animals, nor did I 
see any of them this year before the month of July, and 
then not in such great plenty; but in the month of 
August, their number was much increased. 

[ Observations on Sea-water.| 

The 27th of July, 1676, I betook myself to the seaside, 
hard by the village of Schevelinge.* Finding myself upon 
the shore (the wind coming off the sea, with very warm 
sunshine), and observing the sea-water as well as I could, 
I discovered in it divers living animalcules. I gave to a 
certain person, who went into the sea to bathe himself, a 


‘G.e., anno 1675. 

* dese diertgens waren seer sedig, sonder eenige horten in haer beweginge 
MS. - + + Were very quiet and without motion” Phil. Trans.— 
Oldenburg’s translation is clearly wrong, and entirely changes the meaning 
of this passage. The organisms were probably very small flagellates 
(? Cercomonas sp.): and I imagine that L. is here contrasting their even 
(creeping) movements with the jumping motions of the Cyclidiwm which he 
had previously seen in rain-water.—According to Sewel (1708), hort means 
“a Hunch, push, jog, tug”: and to do a thing “ met horten en stooten”’ 
signifies to do it “ by fits and starts”, as we now say. 

* Presumably 1675-1676. 

* Now called Scheveningen—the well-known sea-side resort near The 
Hague: but the name is so spelled by L. here and elsewhere (cf. Send-brief 
XLII, 10 Sept. 1717), as it is in some old Dutch maps which I have 
examined. Pepys, in his Diary, also calls the place ‘ ‘ Scheveling, ” while 
Temple (1693), our Ambassador to Holland in 1668, writes ‘Skeveling ”’ ; 
and Professor Beijerinck informs me further that the spelling © Schevelingen ”’ 
was sometimes used formerly. The appearance of the ‘‘ Shore at Schevelinge ”’ 
in L.’s day is shown in the well-known picture by Jacob van Ruisdael (1628- 
1682) in the National Gallery (No. 1390). See Plate XXI. 



new glass phial (which I had bought on purpose) and 
besought him that, when he was in the sea, he would 
rinse it out twice or thrice and then fill it up with water. 
This having been carried out according to my orders, I 
tied the phial up tight with a clean bit of bladder: and 
on reaching home and examining the water, I perceived 
therein a little animal’ that was blackish, having a shape 
as if twere made of two globules. This little animal had 
a peculiar motion, after the manner of a very little flea, 
when seen, by the naked eye, jumping on a white paper ; 
yet ’twas only displaced, at every jump, within the com- 
pass of a coarse sand-grain, or thereabouts. It might 
right well be called a water-flea; but ’twas not so big, 
by a long way, as the eye of that little animal which 
Swammerdam calls the Water-flea.” 

I did also discover animalcules which were clear, of the 
same bigness as that first mentioned; but they had an 
oval figure, and their motion was snake-wise. 

Furthermore, I perceived yet a third sort, which were 
very slow in their motion. Their body was mouse-colour ; 
and they were also a bit on the oval side,’ save that a 
sharp little point stuck out (sting-fashion) * in front of the 
head, and another at the hind end. This sort was a bit 

And there was besides a fourth sort, rather longer than 
an oval. Yet all these animalcules were few in number, 
so that in a drop of water I could make out but 3 or 4, 
nay, sometimes but one. 

* Iam unable even to hazard a guess at the identity of this organism ; 
but, judging from its estimated size, it may well have been a protozoon. 

> i.e., Daphnia. Cf. p. 118, note 1. 

° mede hellende na de ovale kant MS. “clear towards the oval-point ”’ 
Phil. Trans.—an evident mistranslation. LL. means that their shape tended 
to be oval—not that they were clear at one end. I translate his colloquial 
old Dutch into its equivalent in modern conversational English. 

* angels gewijs MS. “‘angle-wise” Phil. Trans. Angel means a sting 
(e.g., that of a bee), not an angle (=hoek). lL. was probably thinking of the 
mouth-parts of a mosquito—which he also called (as the man-in-the-street 
still does) its “‘sting”’. ; 



The 31st ditto, having examined this water every day 
since the 27th, and perceived no little animals in it; 
upon this date I did now see a good hundred of ’em where 
at first I had seen but one: but they were now of another 
figure, and not only smaller, but also very clear. They 
were like an oblong oval, only with this difference, that 
they tapered somewhat more sharply to a point at what 
I imagined to be the head end. And although these were 
at least a thousand times smaller than a very small sand- 
grain, I saw, notwithstanding, that whenever they lay 
high and dry out of the water they burst asunder, and 
flowed apart or scattered into three or four very small 
globules and some watery matter, without my being able 
to discern any other parts.’ (In the above, I took the 
water out of the phial from the surface: and at this time, 
too, I was no longer able to see the animalcules of the 
sort first spoken of.) 

The 2nd of August I could discern nought but an 
abundance of the foresaid animalcules. 

The 4th ditto, saw ’em as heretofore, without any 

The 6th of August, looking again, perceived nowhere 
near as many little animals. 

The 8th ditto, I again discovered a very few of the 

. foresaid animalcules; and I now saw a few so exceeding 
small that, even through my microscope, they well-nigh 
escaped the sight. And here I stopped my observations.” 

[Observations on Pepper-water. Ist Observation. | 

Having made sundry efforts, from time to time, to 
discover, if ‘twere possible, the cause of the hotness or 
power whereby pepper affects the tongue (more especially 
because we find that even though pepper hath lain a 

’ This observation indicates that the organisms were protozoa. 

* Beyond the obvious fact that they were probably protozoa and bacteria, 
I cannot offer any guess at the identity of the various organisms which L. 
saw in sea-water. 


whole year in vinegar, it yet retaineth its pungency); I 
did now’ place anew about 3 ounce of whole pepper in 
water,’ and set it in my closet, with no other design than 
to soften the pepper, that I could the better study it. 
This pepper having lain about three weeks in the water, 
and on two several occasions snow-water having been 
added thereto, because the water had evaporated away ; 
by chance observing this water on the 24th April, 1676, 
I saw therein, with great wonder, incredibly many very 
little animalcules, of divers sorts; and among others, 
some that were 3 or 4 times as long as broad, though 
their whole thickness was not, in my judgement, much 
thicker than one of the hairs wherewith the body of a 
louse is beset.2 These creatures were provided with 
exceeding short thin legs in front of the head (although 
I can make out no head, I call this the head for the 
reason that it always went in front during motion). 
This supposed head looked as if ’twas cut off aslant, in 
such fashion as if a line were drawn athwart through 
two parallel lines, so as to make two angles, the one of 
110 degrees, the other of 70 degrees. Close against the 
hinder end of the body lay a bright pellet, and behind 
this I judged the hindmost part of all was slightly cleft. 
These animalcules are very odd in their motions, oft-times 
tumbling all around sideways; and when I let the water 
run off them, they turned themselves as round as a top, 
and at the beginning of this motion changed their body 
into an oval, and then, when the round motion ceased, 
back again into their former length.’ 

cis Bi ate Fie i 5 

! The exact date is not recorded ; but it will be seen from the next sentence 
that the pepper was laid in water during the first few days of April, 1676. 

® Unfortunately L. omits to state what kind of water he used. Had he 
done so, it would have afforded some help in attempting to determine the 
organisms which he found in it later. 

* About 3. See p. 337 infra. 

‘From the foregoing description I think it highly probable that the 
animal observed was Bodo caudatus (Duj.) Stein,—one of the commonest 
protozoa found in organic infusions. The description, as far as it goes, fits 
this animal almost exactly. 


The second sort of animalcules consisted of a perfect 
oval." They had no less nimble a motion than the 
animalcules first described, but they were in much 
greater numbers. And there was also a third sort, which 
exceeded both the former sorts in number. These were 
little animals with tails, like those that I’ve said were in 

The fourth sort of little animals,’ which drifted among 
the three sorts aforesaid, were incredibly small; nay, 
so small, in my sight, that I judged that even if 100 of 
these very wee animals lay stretched out one against 
another, they could not reach to the length of a grain of 
coarse sand*; and if this be true, then ten hundred 
thousand of these living creatures could scarce equal the 
bulk of a coarse sand-grain. 

I discovered yet a fifth sort,’ which had about the 
thickness of the last-said animalcules, but which were 
near twice as long. 

2nd Observation [on Pepper-water]. 

The 26th of April,° I took 23 ounces of snow-water 
(which was a good three years old, and which had stood 
throughout either in my cellar or in my closet in a glass 
bottle, well stoppered), wherein I was able to discover no 
living creatures. Having poured this same water into a 
porcelain tea-cup, with half an ounce of whole pepper, I 
set it likewise in my closet. J examined this water every 
day until May the 3rd, but could discover therein no 
living creatures; and by now the water was so far 
evaporated away and absorbed by the pepper, that some 

* Perhaps a Cyclidiwm—equally common in infusions of all sorts. 
* Vorticella sp. Cf. p. 118 supra. 
* Evidently bacteria. 

*T.’s “coarse sand-grain’’=approximately 355 inch in diameter. Cf. 
p. 334 enfra. 

> Probably bacilli. / 
* i.e., anno 1676. le 


of the pepper-corns began to lie dry. And this water was 
now so thick with particles, that you might almost 
imagine you were looking at the spawn of very wee fish, 
what time the fish discharges its roe, when the roe-corns 
are very soft, and as ’twere hang together. Thereupon 
I added snow-water to the pepper once more, until the 
pepper-corns lay under about half an inch. 

The 4th and 5th of May, examined it again, but 
perceived no living creatures. 

The 6th ditto, I discovered very many exceeding small 
animalcules.' Their body seemed, to my eye, twice as 
long as broad. Their motion was very slow, and oft-times 

The 7th ditto, I saw the last-mentioned animalcules 
in still greater numbers. 

On the 10th ditto, I added more snow-water to the 
pepper, because the water was again so diminished that 
the pepper-corns began to lie dry. 

The 13th and 14th ditto, the animalcules as before. 

The 18th of May, the water was again so dried away, 
that I added snow-water to it once more. 

The 23rd of May, I discovered, besides the foresaid 
animalcules, living creatures that were perfectly oval, like 
plovers’ eggs.” I fancied that the head was placed at the 
pointed end, which at times was stuck out a bit more. 
Their body within was furnished with some 10, 12, or 14 
globules, which lay separated from one another. When 
I put these animalcules on a dry place, they then changed 

" Probably bacilli. 

® de Kievits eijeren gelijk MS. “like Cuckow-eggs”’ Phil. Trans. Kievit 
means the Peewit or Lapwing (Vanellus cristatus), not the Cuckoo (Cuculus 
canorus). The eggs of the former are, of course, those which are known 
commercially as “ Plovers’ eggs”. The distinction is not without import- 
ance here, as the “ Plover’s egg” is conspicuously pointed—that of the 
Cuckoo being much more rounded.—The organism was probably Colpidium 
or an allied ciliate. L.’s remarks a little later support the view that he was 
observing the “small variety’ of C. colpoda—a very common inhabitant of 
such infusions. 


their body into a perfect round, and thereupon oft-times 
burst asunder; and the globules, together with some 
watery humour, flowed out on all sides, without my being 
able to discern any other remains. These globules, which, 
in the bursting asunder, flowed apart from one another, 
were of about the bigness of the first-mentioned very 
little animalcules. And albeit I could as yet distinguish 
no feet on the said animalcules, none the less I imagined 
that they must be furnished with many very little ones ; 
for the very smallest animalcules (whereof I have already 
said there were a great many in this water, and of which 
more than 100 sometimes lay around one of the little oval 
creatures) were driven away from the bigger ones by the 
motion which these made in the water (even when the 
big animalcules themselves seemed to me simply to lie 
still, without stirring at all), just as if you were to blow a 
feather from your mouth.’ Of these oval animalcules I 
could never discover any very little kind,’ how diligently 
soever I sought them. 

The 24th ditto, examining this water again, I found the 
oval animalcules in a much greater number. Dvtto, in 
the evening, looking again, I perceived so great a plenty 
of the oval animalcules, that ‘twas not a mere thousand 
that I saw in one drop; while there were several thousands 
of the very small animalcules in the same drop. 

The 25th ditto, I saw still more of the oval animalcules, 
and some most exceeding thin little tubes,’ which I had 
also seen many a time before this. 

The 26th ditto, I saw such a great many of the oval 
creatures, that I believe there were more than 6 or 8 
thousand in one drop, not counting the multitude of very 
little animalcules, whereof the number was far greater. 

SS, - aE 

1 This is obviously a description of a ciliate (e.g. Colpidium), with actively 
vibrating cilia, lying among bacteria. 

® f.e., any young ones. 

* pijgpjes MS. Probably thread-bacteria. 


But I took this water from the surface, and in the water 
that I took from underneath there were nowhere near as 
many. Seeing these little animals increase to so vast a 
number, but therewithal not being able to detect that 
they did wax in bigness, nor yet to espy any like creatures 
drifting in the water, I bethought me whether these 
animalcules might not well be put together in an instant 
(so to speak) *: but this speculation I leave to others.” 

The 26th dztto, in the evening, I perceived almost none 
of the little animalcules; but I now saw divers creatures 
with tails (whereof I have said heretofore that I saw ’em 
in rain-water).” And furthermore I saw one animalcule 
that was three times as long as broad. Through all the 
water floated numberless particles, like thin little hairs 
off men who haven’t been shaved for a fortnight*; but 
with this difference, that many had a kink in them. 

The 27th ditto, I perceived none at all of the very little 
animalcules, but the large creatures in greater number. 

The 28th ditto, almost all the animalcules in the pepper- 
water were become somewhat scantier.’ 

The 80th dztto, I discovered very few animalcules in 
the water, and I saw there now but one where some days 
before I had seen a good hundred. And as the water was 

' of deselvige niet wel in een moment des tijts (om soo te spreeken) en 

waren te samen gestelt MS. He means that it crossed his mind that these 
animals might possibly come into existence, on a sudden, by a fortuitous 
concourse of inanimate particles in the water. As a rule, of course, L. 
strongly opposed the doctrine of spontaneous generation. 

* dog ik geef dit aen anderen over MS. 
* i.e., Vorticella sp. 

* By this quaint simile L. means to convey the idea that the particles, if 
magnified in diameter to the size of human hairs, would be about as long, 
in proportion, as those forming the beard of a normally clean-shaven man 
who had not shaved himself for about a fortnight. 

> wat dunder MS., lit. = somewhat thinner. I take L. to mean that the 
water itself was now not so full of animalcules—not that the animalcules 
had themselves grown thinner. But Oldenburg seems to have taken the 
latter view, for he translates (Phil. Trans.) ‘all sorts of those living creatures 
in this peppery water were grown thinner.” The ensuing paragraph supports 
the above reading. 


now so dried away, that the pepper began again to he 
above the surface, I filled up the tea-cup with snow-water 
once more. 

On June the Ist, the animalcules were again in as 
great numbers as I had ever before seen, though I can’t 
say that I saw any of the very little ones. But now I 
could see very plain that the animalcules were furnished 
with very thin little legs,* which was a very pretty sight 
to see. 

The same day, I discovered some few very little round 
animalcules,’ that were about 8 times as big as the 
smallest animalcules of all. These had so swift a 
motion before the eye, as they darted among the others, 
that ’tis not to be believed. The big creatures, which 
were about 8 times smaller than the eye of a louse,’ were 
in no less number. 

My further observations on this water I have made no 
note of. 

8rd Observation [on Pepper-water]. 

On May the 26th, I took about $ of an ounce of whole 
pepper, and pounded it small, and then put it in a 
tea-cup in which there was about 22 ounces of rain-water, 
stirring this water about in order that the pepper might 
mix itself with the water and then sink to the bottom. 
And after letting it stand thus an hour or two, I took 
some of the forementioned water in which the whole 
pepper lay, and which contained a multiplicity of little 
animals, and mixed it with this water wherein the 
pounded pepper had now lain for one or two hours: and 


i.e., the cilia on the ciliates (? Colpidiwm). 
* Probably larger bacteria. 

* This is the first indication which L. gives of the size of his ciliates. 
‘About 8 times smaller’? means “having a diameter of about a half”: 
and this therefore agrees with the supposition that the “ oval animalcule”’ 
was the small species (or variety) of Colpidiwm so commonly found in 
such infusions. 


I observed that when I added rather much of the water 
containing the pounded pepper, it came to pass that the 
foresaid animalcules died forthwith; but when I added 
somewhat less of the same water, then the little creatures 
remained alive. 

On June 2nd, in the forenoon, after I had made divers 
observations since the 26th ultimo, but without being 
able to discover any living creatures, I now saw a few 
particles which had, indeed, the figure of some of the 
little animals, although I could distinguish no life in 
them, how attentively soever I looked. On the 2nd 
again, at night, about 11 o’clock, I discovered a few very 
little living animalcules. 

The 3rd ditto, I discovered therein many more 
animalcules, which were all very small, and about 2 or 8 
times as long as broad.’ All through this water little 
bubbles kept rising, as if ’twere fresh beer that stood 

The 4th ditto, in the morning, I found therein a great 
many animalcules. The same day, in the afternoon, 
examining the water again, I saw such a great many 
living creatures in one drop of it, that they amounted 
to at least 8 or 10 thousand; and to my eye they were, 
when viewed through my microscope, like ordinary 
sand-grains to the naked eye. 

On the 5th ditto, I discovered, besides the multifarious 
very little animalcules aforesaid, some few (but not above 
8 or 10 in one drop of water) little oval animals,” whereof 
some exceeded the others quite 8 times in bigness,’ whilst 
the biggest of them were in shape like the oval 
animalcules that I have made mention of before (those 
that were in the water wherein the whole pepper lay).* 

* s00 lang als breet MS. “as broad as long” Phil. Trans.—an obvious 
mistake.—The organisms were evidently bacilli. 

* Probably Colpidium again. 

* 1.e., were twice as long. 

* i.e., they resembled the organisms previously identified as Colpidiwm. 


On the 6th ditto, the animalcules were as before. 

On the 8th ditto, the little oval animals* were 
multiplied, swimming among the foresaid very numerous 
little animalcules*; and now they’ were very nearly all 
of one and the same bigness. 

The 9th of June, the oval animalcules were in yet 
ereater number, but the very little animalcules were now 
less. And now, using again a particular method in 
observing, I saw the little feet or legs* (wherewith the 
animalcules were provided underneath their body, which 
was flat) moving very plainly ; and with such a swiftness, 
that ’tis incredible. And methinks that ever and anon I 
could make out that each of the globules, whereof, as I 
have said, their body was for the most part composed, 
was not perfectly round, but every one of them stuck out 
in a point, in the same fashion as the shields or plates 
on the sturgeon or thornback do.’ The said animalcules 
were, to my eye, 8 times smaller than the eye of a louse.” 

On the 10th ditto I took a little of the last-mentioned 
water, and mixed it with a little water wherein 36 cloves 
had now lain for about 3 weeks; and I perceived that, 
no sooner did the multifarious little animals aforesaid 
come into this mixed water, than they were dead. 

On the 12th ditto, the said animalcules seen in no less 
number; and as the water was now so evaporated away 
and sucked up by the pepper, that the pepper itself began 

* Colpidium. 
* Bacteria. 

*¢.e., the colpidia. L. cannot have meant that the ciliates and bacteria 
were now equal in size. 

‘ i.e., the cilia (on the Colpidium). 
° ie., like the “ placoid scales ” of some Ganoid and Elasmobranch fishes, 
such as the sturgeon (Acipenser) and the thornback (Raja clavata). 

® This estimate accords with that given for the “ oval animalcules ’’ under 
date June 1 (2nd observation).—Oldenburg’s translation in the Phil. Trans. 
terminates at this point. All that follows has never previously appeared in 






to lie dry, I threw the latter away, after first of all tasting 
it on my tongue, and finding it as strong as if it had just 
been pounded. 

4th Observation {on Pepper-water |. 

The 14th of June, a certain quantity of whole pepper 
put in well-water. 

The 16th dzttv, in the morning, on examining the same, 
I discovered, in a tiny drop of water, incredibly many 
very little animalcules, and these of divers sorts and sizes.’ 
My further observations I have not made note of, save 
that on the 17th of July still more animalcules were seen, 
and among them many of the little oval creatures” many 
times mentioned already. 

Examining the water again on July 20th, I now saw, 
with very great wonder, that some very long and very 
thin particles (which I imagine had come to my notice 
in various waters before) were alive. These most 
wonderful living creatures seemed, when viewed through 
my microscope, thinner than a very fine hair of one’s 
head, and about as long as the back of a bread-knife,° 
others quite twice as long. Their whole body appeared 
of one and the same thickness throughout, without my 
being able to make out a head or any bodily parts; and 
therewithal their body was very clear, and ’twas thus 
very troublesome to succeed in seeing ’em alive in the 
water. They moved with bendings, as an eel swims in 
the water; only with this difference, that whereas an eel 
always swims with its head in front, and never tail first, 

Bacteria—various sorts. 
Another of L.’s homely similes. He means that the “animalcules” 

were very long, and uniformly thin—their proportions being similar to those 
of the blunt edge, or back, of a large knife such as is used for cutting bread ; 
though their thickness actually appeared not so great, but even less than 
that of a human hair as seen by the naked eye. Itis a peculiar comparison, 
but on the whole conveys a tolerably accurate notion of the appearance of 
the long thread-bacteria which he was evidently observing. 


yet these animalcules swam as well backwards as forwards, 
though their motion was very slow. And were I to 
contrast these creatures with the eels or worms which are 
in vinegar,’ I imagine the proportions would be thus : 

As a worm of the bigness of a big pin, is to an eel of 
the thickness of one’s wrist : So are these very little living 
creatures or eels in the pepper-water, to the size of the 
eels in vinegar. 

5th Observation [on Pepper-water]. 

On August the 2nd, in the evening about 7 o’clock, I 
again examined my well-water, which was very clear 
(especially when it stood in a kettle or pot; but standing 
in a clean glass, alongside of clean rain-water, the rain- 
water outdid the well-water in clearness). In this well- 
water I saw living a great many of the oft-mentioned 
very little animalcules*; some thousands, indeed, in one 
drop of water. I then poured some of this water into a 
porcelain tea-cup, adding thereto a quantity of coarsely 
pounded pepper; and [I stirred round the pepper in the 
water, deliberating whether the said animalcules would 
remain alive in the peppery water, or whether they would 
die. This water and pepper having been stirred up, I 
examined it, and saw the animalcules living: after the 
lapse of half an hour I examined it again, and saw the 
animalcules still alive, but their motion was not so quick 
as when they were in plain well-water. After the lapse 
of two hours more, examining the water again, I saw the 

ee ee 

1 A yemarkably shrewd observation, which proves conclusively that L. 
was here dealing with bacteria. The organisms were evidently the long 
flexible thread-bacteria (Pseudospira C.D.) so common in infusions. 

2 Of these more anon. The “vinegar-eel” (Anguzllula acett) was 
described by L. in an earlier letter, dated 21 April 1676. See Phil. Trans., 
Vol. 0%, p: 6093 (1676). Power, Kircher, Borel, and others had, however, 
discovered this organism at a still earlier date, though L. was apparently 
unaware of their observations. IL. gives figures of the eel in a later letter 
(No. 43, 5 Jan. 1685). 

® fe., bacteria, in all probability. 


animalcules even yet alive, though in much less number 
than heretofore. 

On the 3rd of August, about 7 o’clock in the morning, I 
saw some few animalcules still alive; while the water was 
fermenting, as if it had been beer that stood and worked. 
In the afternoon, about 4 o’clock, examining it again, I 
still saw a few animalcules alive. In the evening, at 
about 9 o’clock, however, I saw very few animalcules 

On the 4th ditto, about 6 o’clock in the morning, I 
could discover no living animalcules, how attentively 
soever I looked; but I thought I saw some floating dead. 
The evening of the same day, about 9 o’clock, I discovered 
4 or 5 very little animalcules, and among them one some- 
what bigger, and very round. Such an animalcule I have 
never seen in well-water. 

The 5th ditto, in the morning, I saw again 4 or 5 very 
little animalcules, among them one that exceeded the 
others a bit in length: and amidst the very many par- 
ticles, I judged that I could distinguish little forms which 
agreed in their shape with the foresaid living animalcules, 
but I could discern no life in them. On the afternoon of 
the same day, about 3 o’clock, I saw several most extra- 
ordinarily small animalcules (nay, even smaller than 
those in the well-water), together with many animalcules 
that were somewhat bigger. These last * were well-nigh 
round, and their motion was mostly all a-rolling, where- 
withal they didn’t much hurry themselves. ‘Together 
with these was a sort” that were of the same size, but 
they were somewhat elliptical. And lastly, I also saw 
some® (though very few) which were a good 20 times 
bigger than the biggest sort spoken of above. These were 

1 Probably small flagellates (? Monas sp.). 
? Unidentifiable. Perhaps more elongated specimens of the same Monas. 

* Perhaps Euplotes or an allied hypotrichous ciliate. (The movements 
described indicate that it cannot have been a Cyclidiwm.) “ A good 20 times 
bigger’? means “ having about thrice the diameter” of the former sort. 


long, and bent crooked, the upper part of the body round, 
but flat beneath, looking much after the fashion of an 
s part of the peel of a large citron. Their motion was all 
a-wallowing, on their back as well as on their belly. I 
could discern no little feet or legs on them; and after this 
time, moreover, I never saw them any more. In the 
evening, about 10 o’clock, I saw the very little animal- 
cules, and the round ones,” in much greater numbers; 
together with a little animal that was 3 or 4 times as 
long as broad *; and besides these, many little worms, or 
little eels *, which were even smaller than the very tiny 
eels spoken of before. 

On the 6th ditto, about 6 o’clock in the morning, [ 
discovered a very great many (indeed, incredibly many) 
exceeding little animalcules, to which, because of their 
littleness, no shape can be given’; and with these a very 
great number of round animalcules,’ which to my eye 
seemed quite eight times as big as the first animalcules (in 
which I have just said I could make out no shape). These 
round animalcules I imagine to be more than 50 times 
smaller than the eye of a louse. And besides these there 
was a third sort,’ that were twice as long as broad, and 
which had about the length of the round animalcules. 
The fourth sort * was the very tiny eels; but now I could 
not see their bending, when they moved, so very plainly 
as I had seen it before: and at this time too I saw some 
(though very few) animalcules, which had very nearly the 
length of the eye of a louse, and which were in shape very 

" Bacteria. 
° 9? Monas sp. 

* Unidentifiable; ? a small flagellate. (Had it been large, L. would 
doubtless have supplied some further details.) 

* Bacteria, probably Spzrzllwm sp. 

> Bacteria. 

° Larger bacteria ? (“8 times as big” = of twice the diameter.) 
* Unidentifiable. 

* Spirilla. 



much like (only much smaller) that animalcule which I 
have previously likened to a piece of citron-peel. More- 
over, I could not convince myself that I now saw, among 
the sorts of animalcules described, those creatures which I 
have said I saw in the well-water, although I examined the 
well-water also. 

The same day, about 3 o’clock in the afternoon, I saw 
still more animalcules, both the round ones and those that 
were twice as long as broad; and besides these, a sort 
which were still smaller ; and also incredibly many of the 
very little animalcules whose shape, this morning, I could 
not make out. J now saw very plainly that these were 
little eels,, or worms, lying all huddled up together and 
wriggling; just as if you saw, with the naked eye, a 
whole tubful of very little eels and water, with the 
eels a-squirming among one another: and the whole 
water seemed to be alive with these multifarious animal- 
cules. This was for me, among all the marvels that I 
have discovered in nature, the most marvellous of all; and 
I must say, for my part, that no more pleasant sight has 
ever yet come before my eye than these many thousands 
of living creatures, seen all alive in a little drop of water, 
moving among one another, each several creature having 
its own proper motion: and even if I said that there were 
a hundred thousand animalcules in one small drop of 
water which I took from the surface, I should not err, 
Others, seeing this, would reckon the number at quite 
ten times as many, whereof I have instances; but I say 
the least. My method for seeing the very smallest 
animalcules, and the little eels, I do not impart to others ; 
nor yet that for seeing very many animalcules all at once ; 
but I keep that for myself alone. 

The same day, about 11 at night, the animalcules were 
as before. The sort in which I could hitherto discern no 
shape, I now fancied to be round, rather than long. 

* Spirilla. 


On the 7th ditto, about 8 o’clock in the morning, the 
animalcules were as heretofore. The little eels or worms 
were a bit bigger, but the very smallest animalcules I 
could not now make out. Ditto, in the evening about 
8 o’clock, I now saw again the smallest animalcules of 
all, but few in number. The round animalcules very 
plentiful; and the animalcules which were twice as 
long as broad, together with the little eels, I saw in 
numbers unspeakably vast, for the amount of water. 

The 8th ditto, about 8 in the morning, the animalcules 
as before. The same day, afternoon and evening, the 
animalcules seen in no less number. 

The 9th ditto, in the morning, the animalcules as 
before. Ditto, in the afternoon, the animalcules in no 
less number, excepting that the round animalcules 
now seemed fewer to my eye. 

Having been, from the 10th to the 17th of this month, 
in Brabant and elsewhere for a holiday, I now observed 
that the water was very small in amount, and thick 
with all manner of very small particles; and I saw that 
the animalcules lay alongside one another in great plenty, 
without any motion, save 2 or 3 animalcules which I saw 
moving feebly. Thereupon I again added a little well- 
water to the pepper and the water that remained over: 
and I then viewed the water, but notwithstanding could 
perceive no further movement in it, after several 

The 18th ditto, in the morning, examining this water 
again, I saw the animalcules alive and moving in as 
great numbers as ever heretofore, though their motion 
was not so quick; excepting only the little eels, none of 
which I could discern. Ditto, in the evening, the motion 
in the animalcules was as quick as ever before. 

The 19th ditto, the animalcules as before. 

The 20th ditto, the animalcules as before. 

The 21st ditto, the animalcules aforesaid, that were 
almost round, were in incredibly great plenty, and more 




than ever before; the animalcules that were twice as long 
as broad were fewer in number than hitherto, and now I 
could discern that before and behind they ran somewhat 
to a point; and ’twas pretty to behold the motion, all 
a-quivering and a-shivering, that such very little creatures 
made in going forward. No others than these two sorts 
could I discover. Among other particles, there drifted 
through the liquid a multitude of short straight little 
tubes, several times (yea, 3 or 4 times) shorter than 
the foresaid very thin little eels or worms, so that they 
were only to be made out by very curious inspection. 

The 21st ditto, in the afternoon, the animalcules in 
abundance, as before. The long animalcules are clear; 
the rounded ones appear encircled with a dark streak, and 
having at the hindmost part of their body a little dark 
spot or point. 

The 22nd ditto, the animalcules as before. The short 
and very smali tubules were in greater numbers. 

The 3rd of September, the animalcules being as before, 
without my being able to espy any notable change in 
them, I again poured well-water (in which there were 
many living animalcules) upon the pepper, and at the 
same time put also two eggspoonfuls of coarsely pounded 
pepper into the water; considering whether the animal- 
cules might not then die. 

* (L have, moreover, well-water containing whole pepper 
still standing in my closet; but I have sent no notes of 
the observations made thereon. I have seen in it, besides 
divers animalcules, a great many little eels or little 
worms, together with a sort of little animals that were a 
bit smaller than the oval creatures already oft-times 
referred to. These were rounded like an oval at the hind 
end of the body, but their foremost part had, at its end, 
a crooked bend, like a parrot’s beak.” 

*The whole of this passage is thus put in parenthesis in the MS., and 
was perhaps meant for a footnote. 

* Probably Chilodon. 


The animalcules which I have throughout called “ oval 
animalcules”’, are not really oval, unless you look upon 
them on the back or upper part of their body; and as the 
making of observations is well-nigh a study in itself, I 
have only just now exhibited them to myself very prettily 
in side-view, and have demonstrated not only their little 
feet, but also their head, and their very short and pointed 
little tail. At such perfection in this tiny creature I did 
creatly marvel’: and were it not that the multiplicity 
of solid particles (which are present in plain water) 
hindered me, I could describe the little animals even more 

The 4th of September, the animalcules were seen in 
such great abundance as never before; but whether the 
animalcules which were at first present in the well-water 
were yet alive, I still can’t say for certain. 

The 5th ditto, the animalcules in an incredible number, 
much greater than hitherto; but they consisted of only 
two sorts, to wit: the roundish animalcules, and the 
animalcules that were twice as long as broad, albeit some 
few somewhat exceeded the others in length. The long 
animalcules were a bit thicker than the hair of a louse, 
and the round ones about twice as thick. 

The 6th ditto, the animalcules in as great abundance 
as heretofore. I now imagined that the long animalcules 
consisted of two sorts: and I imagined, furthermore, that 
I saw animalcules of such extreme littleness as I had 
never up to this date seen in pepper-water. 

The 7th ditto, the animalcules in even greater number 
than before this date. 

The 8th of September, besides the foresaid long animal- 

1T, was always carried away with delight at beholding the “ perfections ”’ 
of ‘little animals’’. So also, it appears, was his draughtsman: for L. tells 
us elsewhere that in making drawings of a flea he was repeatedly provoked 
to exclaim (his words being given by L. in large capitals) “‘ Lieve God wat 
sijnder al wonderen in soo een kleyn schepsel!” (Letter 76, 15 Oct. 1693.) 
Cf. also p. 279 znfra. 



cules and roundish animalcules, I discovered three which 
had the figure of a pear, only with this difference, that on 
the underside of their body they were flat.’ Such a sort I 
had not seen till now in any water. And I had such a 
hunt for these creatures, because they were so few, that I 
gave no heed to the very smallest ones. 

The 9th ditto, I perceived but one of the animalcules 
that had the figure of a pear, in four several observations. 
And though there was still quite a lot of water with the 
pepper, yet I added more well-water to it, because the 
pepper-water was become rather thick. Ditto, in the 
afternoon, about 4 o’clock, I could see none at all of 
the animalcules that had been in great plenty in the 
well-water ere I poured it on the pepper; neither could 
I discover any of the animalcules that had the figure 
of a pear. 

The 10th ditto, in the morning, the roundish and the 
long animalcules were now in such inexpressibly great 
crowds, that they far exceeded in number all the animal- 
cules that I had ever seen up to this date in any waters. 
Moreover, I could discern no other sort. 

On the 14th ditto, I could remark no change since the 
10th, save only that 1 now saw again animalcules which 
had the figure of a pear; and I saw there besides an 
animalcule with a tail.’ 

The 15th ditto, | saw more animalcules that had the 
figure of a pear, and two or three animalcules with tails. 
And I perceived at this time that the pear-shaped 
animalcules kept not against the surface of the water, 
like the other creatures, but that they swam a bit deeper 
under water. Their thickness was about that of a single 
small thread of a silk-worm,’ and they were about 13 times 

’ Evidently a hypotrichous ciliate. 

? t.e., Vorticella. 

° Cf. Letter 146. 20 April 1702. To the Landgrave of Hesse. Printed 
fully in Dutch and Latin collective editions. 


as long as broad. The smaller nearly round animalcules, 
and the long ones, were present in no less number. 

The 16th ditto, the animalcules that had the figure of 
a pear, as before: the animalcules with tails were 
increased to a greater number: the small round animal- 
cules, and the animalcules that were twice as long as 
broad, were now diminished in number. 

* [The 16th ditto, the animalcules that had the figure 
of a pear, as before: the animalcules with tails were even 
more numerous than formerly: the long and the round 
small animalcules were even more reduced in number. | 
On this occasion I discovered three animalcules’ that 
were equally thick throughout, but which tapered to 
rounded ends before and behind, very like the fruit that 
we call dates.* The thickness of them was about that of 
a very fine sheep’s hair. Their motion was very curious, 
with a rolling about and a tumbling and a drawing of 
themselves together into a round. 

The 17th ditto, the animalcules that had a figure like a 
pear, as before: the animalcules with tails in greater 
number: the long and the round animalcules were de- 
creased still further, and therewithal very slow a-moving. 
The animalcules that were equally thick throughout were 
somewhat more plentiful; and now I could make out 

"The passage here placed in square brackets is in the MS., but it is 
obviously a repetition—with slight differences in wording—of the preceding 
paragraph. lL. seems to have paraphrased the same entry in his notebook 
(for Sept. 16) twice over, by mistake. 

* Evidently a large ciliate—probably Oxytricha. 

*dalen MS. I have been unable to find this word in any dictionary— 
ancient or modern. Oldenburg (MS. ined.) translated the word thus, and 
may have had some authority for so doing. Elsewhere, however, L. speaks 
of the date by its usual Dutch name, dadel: cf. Letter 47, 12 Oct. 1685. 
The description is consistent with the above rendering: and Dr E. P. Snijders 
informs me that candied dates are still sometimes called “ confijte dalen”’, 
in popular speech, in Holland. 

‘ Blsewhere (Letter 80,2 Mar. 1694) L. shows that sheep’s wool consists 
of a number of “ fine hairs” stuck together. By “a fine sheep’s hair’’ he 
here means, apparently, one of these component filaments. 



that they were a bit flat in front, furnished with divers 
little legs, which during motion stuck out a bit beyond 
the body; and at the hind end of the body there was a 
round spot, running out headwards in a dark streak, 
looking very much like the guts or the blood in the 
body of a louse,’ as seen with the naked eye. 

The 19th of September, the numerous long and roundish 
little animalcules were much slower in their motion, and 
amany of them lay without any motion at all. The 
animalcules with tails were increased to yet greater 
numbers: the animalcules equally thick throughout, and 
those that had the figure of a pear, were in number as 

My further observations I have not recorded: I can 
only say this, that in the course of a day or two the 
water again got so thick, that all the animalcules that 
were still in it moved themselves very slow; and 2 or 
3 days after I had poured in well-water once more, I 
perceived the small animalcules in as vast a number as 
ever heretofore. 

[Observations on Vinegar. ] 

For the last 2 or 3 years I have not been able to find 
any little worms, or eels, in the vinegar that I keep in 
a cask in my cellar, for my household. I now®* drew 
off } pint of this vinegar into a glass, and set it in my 
closet, covering it over with a paper to keep off the dust : 
and after the lapse of 11 days, I did perceive therein 
little eels, which multiplied from day to day. I have 
divers times put a little vinegar into a little pepper-water, 
and have always seen that as soon as the pepper-water 

‘4 more particular description of this phenomenon was given by L. in 
an earlier letter (7 April 1674) published—in part only—in Phil. Trans., 
Vol. IX, p. 23. The more famous description of the “blood and guts in the 
louse” by Swammerdam was not published until long after this date. 

* See note 2 on p. 141. 

* No date is here recorded. 


was mixed with the vinegar, the animalcules that were in 
the pepper-water died instantly; albeit that I was unable 
to perceive that the little eels, which were in the vinegar, 
suffered any hurt from the pepper-water. 

At another time I took some 10 parts of the pepper- 
water last spoken of (at the time when the living creatures 
were most plentiful in it), and added to it about 7 part 108 
vinegar, containing living eels, or little worms. This 
vinegar I put in at the bottom, and not on the surface, of 
the pepper-water: and I took note that, the moment the 
vinegar was added to the pepper-water, the multifarious 
very little animalcules that were next the bottom, where 
the vinegar was, lay without any motion; and those 
animalcules lying further from the bottom became slower 
in their motion; and after the lapse of a little while, all 
the very little animalcules were dead: yet the motion of 
the little eels was no less in this water than when they 
were in the vinegar alone. This pepper-water and vinegar, 
which together equalled in quantity one big drop of 
water, I observed almost from day to day: and after the 
lapse of about 2 or 3 weeks, I saw that the little eels in 
this mixed water were greatly increased; for where at 
first I had seen but 10 eels, I now saw fully 200 of ’em. 
And among the rest I saw a great number of very little 
eels, near of one and the same bigness as one another, 
whose length, to my eye, equalled about 1 or t part of the 
biggest eels of all; but notwithstanding the further ob- 
servations that I made, I was able to discover no smaller 
eels, nor yet any particles that looked like the foresaid 
very little animalcules*; but they seemed all gone, without 
any remains being left over. Seeing this multitude of 
little eels (in the mixture of 10 parts pepper-water and 
1 part vinegar), I imagined that surely they were not 

Dee ——— 

1 Ags becomes evident later, L. means that he took 1 part of vinegar 
to 10 parts of pepper-water—not, as he apparently says, one-tenth of a 
part of the former to 10 parts of the latter. 

2 = . 
1.e., bacteria. 


generated from any particles which might have been in 
the pepper-water, nor yet from such as might have been 
in the vinegar, as this, mixed with pepper-water, would 
have become unfit for the production of living creatures : 
but I felt firmly persuaded that the said little eels had 
become thus increased by procreation. I then made use 
of certain means, in order to throw more light on these 
very little animalcules; and first of all, after I had broken 
asunder or pulled apart some of the biggest sort (corre- 
sponding to those that I had seen originally in my wine), 
I saw that they were provided inside with a long structure, 
which had about 4 of the thickness of the eel itself. I 
imagined that this was the gut of the little animal. In 
some, moreover, I saw still much thinner long structures, 
which I imagined might well be small eels: otherwise 
the body of this creature was very soft, and streamed 
away on all sides in many big globules of various sorts, 
and others that were very little (in proportion to the 
animalcule). These globules did not consist of watery 
matter, but were, in fact, oil: for just as clearly as you 
can, by the eye, distinguish oil floating on water, from the 
water itself, so clearly could I see the oily particles, 
among which were some so small that they well-nigh 
escaped the sight. These curiosities of mine I divers 
times followed up further; and at last I saw very plainly, 
among other things, that from an eel which I had broken 
across the middle, there came out four distinct small eels, 
each twisted on itself, very nice and pretty, and each 
bigger than the one following: and the biggest, which 
came out first, lay and lived, and wrenched itself loose, 
and remained alive a little while." I have more than 
once been able to see a small eel, out of an eel which I 

* All these exact observations can be very easily confirmed. The vinegar- 
eel is viviparous; and L. was evidently here dealing with large pregnant 
females, whose larval young drop out and behave just as he says when they 
are torn in two.—These were the first observations ever made on the 
reproduction of Anguwillula. 


had broken in pieces, lie a-writhing, and remain alive so 
long, that it wearied me to keep my eye upon it. I have 
also seen two small living eels come forth from an eel 
after I had cut it in pieces: and they moved themselves, 
and swam, and were in bigness like the smallest sort. To 
sum up, the more observations I made on this matter, 
the clearer did I demonstrate that the small living eels 
come out of eels: and I conceive also that ’tis certain 
I have seen the little eels alive in the big eels; but this 
came to my notice only when I had taken the big eels 
out of the vinegar, and when they lay a-dying.’ 

[ Observations on Ginger-water. | 

The 6th of May, 1676, I put into a porcelain tea-cup, 
which holds a little more than 24 ounces of water, three 
of the ordinary large pieces” of ginger, after I had first 
of all bruised them a bit with a hammer; merely with 
the idea of seeing if the snow-water which I poured on 
the ginger would bring forth living creatures with it. 

The 14th ditto. I observed this water almost every 
day, but till now I could perceive no living animalcules ; 
and by this time the water was so dried up, or drawn into 
the ginger, that I poured fresh water upon it. 

The 29th ditto, having again examined this water 
almost from day to day since the 14th, I now discovered 

* L. at this point enters upon a long digression (about one whole page), 
in which he describes and discusses the structure of the peppercorns them- 
selves and attempts to explain why they have a hot taste. This leads him 
further to discuss the constitution of wheat and other kinds of grain, and 
several physiological problems suggested by his observations. After this he 
suddenly returns to his experiments with infusions, and at this point I have 
resumed my translation. The observations here omitted have no interest 
from a protistological standpoint. 

* clawwen MS. UL. evidently means the broken pieces of the dried 
rhizome of the plant, as commonly sold by apothecaries.—I am informed 
that the irregularly branching pieces of rhizome are known in the trade as 
“hands” of ginger: and I take it that L.’s “ claws” were the broken-off 
“fingers” of such “ hands”’. 


some very little animalcules, a bit longer and bigger than 
the small animalcules seen by me in the pepper-water. 
Nevertheless, these had a different form and motion; 
for while the animalcules in the pepper-water went 
forward all winding-wise, these animalcules all advanced 
in jumps, hopping like a magpie: yet were they very 
few in number.’ 

The 30th of May, observing the ginger-water anew, I 
discovered at least 25 times more animalcules therein 
than previously. Among them were some quite three 
times as long as broad, and I fancied I saw that their 
fore and hind ends were fashioned aslant:; that is, with 
an acute angle and an obtuse angle, as I have said before” 
of a like sort that were bigger. Ditto, about 10 o’clock 
at night, the said animalcules seen in greater number. 

The 31st ditto, the foresaid animalcules seen in still 
much greater number, amounting to several thousand in 
one drop of water: and some of them exceeded the others 
in length. 

The Ist of June, the animalcules seen in still greater 

The 3rd ditto, the animalcules seen in such a vast 
number (in the water that I took from above, off the 
surface of the water), that were I to declare, according to 
my own judgement, how many thousands there were in 
one drop of water, ’twould not be believable. 

The 4th of June, the water was again so evaporated 
away, that the bits of ginger began to lie dry; so I poured 
on rain-water at this time. 

The 10th ditto, upon the water lay a thick film, which 
I took off: and I then saw some oval animalcules,* in size 
and shape like those that I have said were in the pepper- 

" From the description of its jumping movements, this was probably a 
Cyclidium—noted earlier. 

” See p. 132, 1st observation on pepper-water. ? Bodo sp. 
* Ciliates, but otherwise unidentifiable. 



The llth ditto, the oval animalcules were in greater 
number, mostly swimming at the top, against the thin 
film that had come again over the water. On this 
occasion I marvelled to see the violence that the first- 
mentioned little living creatures’ exercised, whenever 
they came out of the water on to a dry place, ere they 
fell a-dying. 

The 12th ditto, the oval animalcules were now in great 
plenty, as well as the other animalcules: and because the 
film that lay upon the water had grown in thickness, I 
poured the water and ginger away.” 

[Observations on Clove-water. | 

On the 17th of May, 1676, I placed 36 cloves in some 
24 ounces of rain-water, after I had first of all examined 
the rain-water and found nought therein (so far as 
animalcules are concerned), save a very few creatures 
that were roundish, and which looked to my eye, through 
my microscope, no bigger than a coarse sand-grain doth 
to one’s naked eye. 

The 25th of May. Up to this date I could perceive no 
living creatures, notwithstanding the many observations 
I had made since the 17th of this month. I now added 
more rain-water (wherein I could discern no animalcules) 
to the cloves. 

The 12th of July. After I had made divers observa- 
tions on this water, and between-times had filled up the 
tea-cup with water once more; and having no thought 
that I should discover living creatures in this water, so 

i.e., those seen on May 29 (? Cyclidiwm). 

? T. again digresses at this point in order to describe the structure of 
the macerated ginger itself. After a long description and discussion— 
occupying more than one whole page of the MS.—he returns to the subject 
of animalcules, and at this point my translation is resumed. Nothing of 
protozoological or bacteriological importance is contained in the lines which 
I have omitted. 




that I did not examine it from day to day, and kept no 
note of when I last added water thereunto: on this date 
I discovered very many living creatures, which displayed 
themselves, through my microscope, as no bigger than an 
ordinary sand-grain to the naked eye. These were very 
clear, and seemed to be about twice as long as broad. 
Along with them were some few animalcules which looked 
as big as ordinary ant-eggs’; the upper part of their body 
being round and raised, the under part flat, like unto 
tortoises in shape. ‘Their whole body seemed to be made 
up of no other parts than big and little globules, which 
were all very glittering, so long as the animalcules were 
alive: but when I brought them into a dry place (where- 
upon they oft-times burst asunder), the glittering went 
off; and the globules became smaller, and flowed away 
on all sides, together with some watery humour in which 
these globules lay. These animalcules were provided 
underneath the body with divers little legs, whereof 5 or 6 
stuck out in front of the head during motion. 

The 14th ditto, I discovered many more animalcules 
than heretofore, but most of them were very small. 

The 19th ditto, I discovered, besides the said creatures, 
many animalcules with tails,” along with many long 
animalcules that were fashioned aslant in front; and if I 
saw aright, their hindmost part was somewhat cloven, 
their body flat below and round above, their length well 
anigh that of the little oval animals. 

The 4th of August, I did not perceive the long 
animalcules, but exceeding many very little animalcules, 
and some few that were a bit bigger. The water being 
now almost evaporated away, I added well-water to it. 

i.e., they appeared, through the microscope, about as big as “ ant-eggs”’ 

appear to the naked eye. (In a later letter L. showed that the structures 
commonly called “ ant-eggs’’ are not really the ova of the ant, but its pupae. 
Cf. Letter 58, 9 Sept. 1687.) From the deseription which follows, they 
were obviously hypotrichous ciliates: but it is impossible to identify them 
more precisely. 

* i.e., some species of Vorticella. Cf. p. 118. 


The 8th ditto, I saw very many animalcules whose 
figure was like an oval, and these were to my eye, through 
my microscope, like coarse sand-grains to the naked eye; 
and there were some few animalcules with tails; likewise 
some little animalcules, and plenty that were bigger, and 
had the length of the eye of a louse. These were bent a 
bit crooked, the underneath part flat; and therewithal 
looking much like an eighth part of a preserved citron- 
peel. Their motion was all turning about, so that I am 
persuaded that they had no little legs; and though they 
were a bit smaller, they resembled very closely the little 
animals previously likened to a piece of citron-peel. So 
great was their number, that it did not amount to a mere 
thousand or two in one drop. 

The 17th of August, the animalcules found as before ; 
but their motion was very slow: and as over a half of 
this water was evaporated away, I added well-water to it 

The 18th ditto, the animalcules as before, and now 
their motion was a bit quicker again; and I now saw 
again more animalcules with tails. 

The 20th ditto, the animalcules with tails were so 
multiplied, that by now they were the most plentiful. 

The 21st and 22nd ditto, the animalcules with tails 
were now less, and their motion, too, was very slow. 
Furthermore, these animalcules with tails, whenever they 
got themselves stuck by the tail in any bit of dirt, 
stretched ’emselves out somewhat longer than the 
animalcules with tails which I have seen in pepper- 
water. The little animalcules were now also less; and 
here and there [ discovered one of the animalcules that 
I have likened to an eighth of a citron-peel. 

The 3rd September, I took one or two cloves out of the 
water, and they were now become so soft that one could 
rub them to bits between one’s fingers: and moreover, I 
found but little savour in them. The animalcules were 
now much decreased, and therefore, as the water was also 




diminished, I poured in well-water, in which were living 
animalcules. After the lapse of an hour, I examined this 
water; and whereas I had seen before very few of the 
animalcules inclining to an oval figure, I now saw many 
of them, together with animalcules that were twice as 
long as broad, besides the animalcules that were in the 
well-water, and a very few animalcules with tails. I 
added 8 fresh cloves to this water, wondering whether 
the animalcules in it would then die. 

The 4th of September, the animalcules as before, 
saving that the animalcules with tails were so diminished, 
that I descried but 2 or 3 of ’em. 

The 5th ditto, the animalcules inclining to an oval 
figure were in greater plenty; and I saw a few of those 
that were twice as long as broad, but none of the animal- 
cules that had been in the well-water, nor of the 
animaleules with tails. 

The 6th ditto, I perceived no other animalcules than 
those tending to an oval. 

The 7th of September, saw animalcules which inclined 
to an oval, without being able to make out any other sort. 
However, they were decreased rather than increased, and 
their motion was not quicker, but rather slower. 

The 8th of September, the motion of the animalcules 
even slower, and they were no more plentiful. 

The 9th ditto, in the morning, at 8 o’clock, the animal- 
cules as before: and because the motion was so slow, 
I added a little well-water. And in this well-water there 
were many very little living animalcules. Dvtto, in the 
afternoon, at 4 o’clock, I now saw the animalcules that 
had been in the well-water still alive in plenty in this 
clove-water; and the other animalcules were now moving 
more lively. Ditto, in the evening at 8 o’clock, the 
animalcules that had been living in the well-water were 
now almost all of them dead; so that I was able to see 
but 2 or 3 alive after several observations. 

The 10th ditto, at 9 o’clock in the morning, no animal- 


cules seen except those inclining to a round oval figure ; 
but the motion of these was a bit nimbler, and they were 
no less in number. 

The 18th of September. The animalcules inclining to 
a round oval figure are got less from day to day since the 
10th of this month, so that at this time I was able to see 
only a very few of them; but now I saw some extra- 
ordinary tiny animalcules, which looked, through my 
microscope, no bigger than common sand doth to the 
naked eye. 

The 19th ditto, stirring the water around a little, and 
then examining it, I saw more of the animalcules likened 
to a round oval than before this date. Along with them 
I perceived the very little animalcules. 

[Observations on Nutmeg-water. | 

The 13th of July, 1676, I beat some big nutmegs in 
pieces with a hammer, and put them in 24 ounces of 
well-water. ‘This well-water I had divers times examined 
during the summer till this date, but could yet discover 
no living creatures in it, save now and then so few and 
extraordinary small, that I did not see them till I had 
made several observations. 

The 17th ditto. Divers observations made since the 
13th of the month, but no living creatures perceived 
therein. And now the nutmegs lay on top, against the 
surface of the water. The water itself lay fermenting, as 
if it had been fresh beer: and betwixt the bits of nutmeg 
lay a lot of round particles of oil, which were very supple. 
These were for the most part 1000 times smaller’ than 
a small sand-grain. 

The 19th ditto, the fermentation was all done with, and 
the nutmegs mostly sunken to the bottom. 


1 je., in bulk: or, in other words, they had a diameter of about one- 
tenth of that of a small sand-grain—on L.’s scale, about one thousandth of 
an inch, or 25. 


The 24th of July, the water was for the most part dried 
up. I again added well-water thereto; and in this well- 
water there were now many very little living creatures,’ 
which, whenever the well-water came under the water 
containing the nutmegs, died in a trice. 

The 3rd of August. Made divers observations since 
the last foregoing date, but discovered no living creatures 
in this water till to-day. The creatures now seen’ were 
very few, and so small, that they well-nigh escaped the 
sight, notwithstanding that one had a very good micro- 
scope. And as the water was, for the most part, dried 
up again, and very many living creatures were at this 
time present in all the common kinds of water, I poured 
on some snow-water, in which there were no animalcules. 

The 4th ditto, the animalcules as before; and they 
moved among so many various particles, of very near the 
same bigness as the animalcules themselves, that you 
would say, ’twas no mere water in which the nutmegs 
lay ; for twas made up of soft fluid particles stuck beside 
one another, much as if you beheld, with your naked eye, 
the spawn of frogs, or the seed of fishes when it is spent.’ 

The 5th ditto, I saw plenty of animalcules, which I 
can’t call long, they looked to me to be round rather ; 
for they were no bigger, through my microscope, than 
very little sand-grains to one’s naked eye; and I must 
say, that I deem them to be a good three or four times 
smaller than the thickness of the hair of a mite, or one 
of the little hairs wherewith the body of a louse is beset." 

The 6th ditto, the animalcules as before. 

The 7th ditto, I saw a huge number of exceeding 
minute animalcules. 

* Probably bacteria and monads. 

* Bacteria. 

? I, doubtless observed, on this occasion, bacterial “ zoogloea’”’ mixed 
with particles derived from the macerated nutmegs. 

‘ Cf. p. 337 infra. The very minute animalcules here mentioned were 
undoubtedly bacteria. 


The 17th ditto, I perceived no animalcules ; and as the 
water was much evaporated away, I added well-water, for 
want of snow-water. 

The 18th ditto, no animalcules made out. 

The 19th of August, many small animalcules seen 

The 20th ditto, the animalcules as before. 

The 21st ditto, the small animalcules seen in greater 
number. I likewise now saw some, though very few, that 
were a bit bigger. These last were very nearly round, 
only tending somewhat to an elliptical figure. 

The 23rd ditto. Besides the said animalcules, I dis- 
cerned, both now and yesterday, divers animalcules that 
were twice as long as broad, running to a point before 
and behind, and of the size of those in the pepper-water ; 
but their motion was not so quivering. I fancied the 
cause of this was that this water was thicker. 

On the 3rd of September, I could perceive no animal- 
cules. The water being now for the most part evaporated 
away, I added well-water, wherein were very many little 
animalcules. I also took a little bit of nutmeg out of the 
water, and tasting it upon my tongue, found it was still 
so strong that it surpassed many fresh nutmegs in savour. 

The 4th ditto, the exceeding very little animalcules 
now seen alive once more. 

The 7th of September, the very little animalcules seen 
alive, as before; yet could I discern no animalcules of 
the sort that were in the well-water ere I put it to the 
nutmegs. My further observations I have not writ 

The objection hath divers times been urged against me, 
that there are, hovering in the air, extraordinary small 
living creatures, which are hid from our eyes, and can 

" The record of observations ends at this point. 


only be discerned by means of surpassing good magni- 
fying-glasses, or telescopes; and these creatures, they 
say, have been seen in Rome.’ For my part, notwith- 
standing the manifold observations I have carried out to 
this end, I have as yet seen no lesser animalcules moving 
in the air than those which are so big that you can 
readily make them out with the naked eye. The very 
little particles which I have commonly found in the air, 
and which are there in motion, are all earthy particles, 
which are given off by (so to speak) “ dustsome ” ’ things. 
For you can’t tear a sheet of paper apieces, but what 
more than a thousand very tiny fibres break off, and these 
so light withal, that they can’t easily fall upon the earth, 
owing to the motion that is in the air: you can’t draw a 
comb through the hair of your head, but what various 
very little particles, which lie or are stuck upon every 
hair, are set loose and moved in the air; not to mention 
the wearing away and the breaking off which each several 
hair suffers in the act of combing. Nor can you so much 
as rub your hands together, when they are dry, nor stroke 
your face, without thereby imparting a multitude of tiny 
scaled-off particles to the air; and ’tis even so with wood, 
earth, smoke, etc. Such particles as these would seldom 
fall upon the earth, so long as they be in the sun’s rays, 
or in a light breeze; but on coming out of the sun’s rays, 
and out of the strong motion of the air, they sink towards 
the earth: and these little bits of dust thus lying still, 
and not sticking to larger particles that are heavier, may 
again be set a-moving by the mere motion of the air, or 
the sun’s rays. From what observations I have made 
hereon, I can’t say I ever saw, among the rest, two bits 
of dust that exactly agreed with one another in shape. 
But I'll not deny that there can be, in the air, any living 
creatures which are so small as to escape our sight; I say 



A rumour, I take it, of the imaginative work of Athanasius Kircher. 
stofligte MS. lL. here invents a word meaning “ apt to form dust.” 


only that I haven’t descried them. And furthermore, I 
am persuaded that they would not be able to remain alive 
in the air, about our horizon; rather would they be 
begotten in the clouds, where, in the continual dampness, 
they could remain alive, and so be conveyed still living to 
us in mist and rain. I fancy I have even seen something 
of the sort in the early summer of this year, on two 
several occasions, when there was a heavy mist here; but 
I saw the supposed creatures without any motion. And 
I believe I have now found out a means of performing 
such observations more exactly and nicely in future. 
These observations concerning living creatures, in the 
liquors spoken of, were indeed deserving of closer atten- 
tion and description ; but for that, there had been need 
too of a whole man, which my circumstances did not allow 
of: for I have employed only my spare time upon them.’ 

Much light is thrown on the observations recorded in the 
foregoing letter by some of the Huygens correspondence. As 
the relevant MSS. are now accessible in print, and as it would 
take us too far afield to discuss the position of Huygens as 
a protozoologist, I shall not now consider this correspondence 
in detail. It is so important, however, that it cannot here be 
ignored, and I therefore add the following notes by way of 

Christiaan Huygens never himself published any serious 
contributions to protozoology: and the records of his own 
observations, which were made in an attempt to repeat 
Leeuwenhoek’s experiments, remained in manuscript and 
unknown until only a few years ago. Consequently, his 
private work” had no influence whatsoever upon the progress 

' A few final remarks—having no bearing upon animalcules—are here 

* Published for the first time in Gwvres Compl. de Chr. Huygens: see 
particularly Vol. VIII (1899), No. 2148, p. 122; and Vol. XIII, fase. ii 
(1916), p. 698 sq. So far as I am aware, all that was previously known 
about Huygens’s protozoological work is contained in the fragmentary notes 
in his Opuscula Posthuma (1703) and Opera Reliqua (1728). These show 
only that he was an imitator of L., and give no idea of the originality of 
his own observations. There is also a reference to the subject in Gregory 
(1713), however, while contemporary mention was made of his observations 
in the Journ. d. Scav. for 1678. 



of protozoology. Had it been published in his lifetime, it would 
have assured him a place in the very forefront of the founders 
of the science. Even at the present moment the excellence 
and originality of his observations have been largely obscured 
by his modern editors. In my opinion most of the protozoa 
described and roughly sketched by Huygens can be easily 
recognized by any competent protozoologist, yet his editors 
have not only failed to recognize the majority but have often 
misidentified common species most ludicrously. As examples, 
I may note that Huygens’s unmistakable account of Chilodon 
(with figures, including a characteristic pair in conjugation) 
is interpreted as “ probably infusoria of the genus Bursaria”’: 
his description of Astasia, with its characteristic euglenoid 
movements and “ hardly any colour”’, is said to suggest the 
bright green and rigid Phacus—“ if having hardly any colour 
be not taken to exclude a slight green coloration’: and so on. 
But we are here concerned with Leeuwenhoek—not with 
Huygens—so I shall say no more on this matter now. I 
hope to deal with Huygens’s admirable observations on another 

Whilst Leeuwenhoek’s astonishing researches were being 
considered by the Royal Society, he himself was continuing 
them and was corresponding with Constantijn Huygens (pater) 
about his discoveries. Sir Constantijn was also in frequent 
communication with his son Christiaan, at Paris, to whom he 
reported Leeuwenhoek’s findings. Christiaan, at first sceptical, 
soon repeated and confirmed the experiments: and at the end 
of 1678 he wrote a most interesting letter,’ accompanied by a 
few sketches, to his elder brother Constantijn. In this letter 
Christiaan gave unmistakable’ descriptions of Chzlodon, 
Paramecium, Astasia, and Vorticella—all found in infusions: 
and he added “I should much like to know what Leeuwenhoek 
would say about all this, and whether he has seen anything 
like them.” Evidently the letter was sent to Leeuwenhoek, 

who wrote to Constantijn Huygens sen. about it a little later.’ 

" Chr. Huygens to Const. Huygens jun. 18 Nov. 1678. Printed in 
Guvres Compl. Vol. VIII (1899), No. 2148, p. 122. 

* To me they are all unmistakable in this description: and when the 
notes of 26 July 1678 (published in Guvr. Compl. XIII (ii), 702) are also 
taken into account, the identifications are surely beyond all doubt. 

* Leeuwenhoek to Const. Huygens sen. 26 Dec. 1678. Letter printed in 
Gwor. Compl. VIII, No. 2156, p. 140. 


Leeuwenhoek here says that he can recognize all the animal- 
cules described by Christiaan, and notes where he had himself 
observed them previously. But he makes one obvious though 
natural mistake: he takes Huygens’s Astasia for the Dileptus 
which he himself discovered, and on which he had observed 
the cilia. Apart from this, Leeuwenhoek interpreted Huygens’s 
protozoa conformably with my interpretations of his own. 
Huygens observed not only the protozoa which Leeuwenhoek 
discovered in pepper-water, but he also saw and delineated 
(his fig. F.) the long thread-bacteria so commonly seen in 
infusions. On these organisms Leeuwenhoek comments : 

These long eels I have seen too. My wonder at these 
animals, was because one was 3 or 4 times as long as 
t’other, yet they were always of the very same thickness ; 
and besides, they swam as well backwards as forwards, 
without my being able to make out any head, or anything 
that looked like a head. I have already written about all 
this to the Royal Society at London’. : 

This is an important passage, as it confirms what Leeuwen- 
hoek had previously said about bacteria. A little later he 
adds the following remarks, with which we may conclude this 
first chapter in Protozoology : 

All these animalcules aforesaid I found too in ordinary 
water, though not so many by a long way as in pepper- 
water. And in the summer, when I feel disposed to look 
at all manner of little animals, I just take the water that 
has been standing a few days in the leaden gutter up on 
my roof, or the water out of stagnant shallow ditches: 
and in this I discover marvellous creatures. 

And whether I put in the water whole white pepper, 
black pepper, coarse pounded pepper, or pepper pounded 
as fine as flour, animalcules always turn up in it, even on 
the coldest days in winter, provided only that the water 
doesn’t get frozen. 

This day [26 December 1678] there are in my pepper- 
water some animalcules which I judge to be quite 8 times 

* See p. 140 above. 




smaller than fig. A.,* on which I can make out the paws 
too, which are also pleasant to behold, because of their 
swift motions. The paws of these animalcules are very 
big, in proportion to their bodies.” Besides these animal- 
cules, I discovered in pepper-water, some few weeks since, 
yet others which I judge to be a good 1000 times less 
than the animalcule in fig. A: for the circumference of 
the whole body of one of these extreme small creatures is 
no bigger than the thickness of a paw of the animalcule 
in fig. A: and I am persuaded that thirty million of these 
animalcules together wouldn’t take up as much room, or 
be as big, as a coarse grain of sand. 

Ajo ee ie Dee TR oy a ein oee DS a eee 
' Referring to Huygens’s sketch of a small (and unrecognizable) ciliate. 

> Ly. probably here refers to the cirrhi on a small hypotrichous ciliate 
such as Huplotes. 




(LETTERS 19, 21, 23, 26, 29a, 30, 31, 32, 33, 71, 92, 96) 

S we have already seen, Leeuwenhoek communicated his 

A discovery of the Protozoa and Bacteria not only to the 

Royal Society but also to Sir Constantijn Huygens. 

The latter evidently wrote a reply—which is lost—to which 
Leeuwenhoek rejoined, inter alia’: 

In order to answer Your Excellency’s letter further, I 
must yet wait 2 or 3 weeks, for the reason that I have to 
repeat the observations I made some time since (concern- 
ing the living creatures in water) with two kinds of 
water, which, among others, I intend to study every day. 

From these words it may be inferred that at the beginning 
of 1677 Leeuwenhoek was still hard at work on his discoveries. 
But the Royal Society also did not remain idle or disinterested : 
the Fellows wanted to know more. Consequently, in an 
editorial comment upon Leeuwenhoek’s observations on the 
animalcules in pepper-water “—wherein he says that he saw 
‘ several thousands of the very small animalcules”’ in a single 
drop of liquid—Oldenburg remarks*: “ This Phaenomenon, 
and some of the following ones seeming to be very extraordinary, 
the Author hath been desired to acquaint us with his method of 
observing, that others may confirm such Observations as these.” 

"From Letter dated 15 February 1677. To Const. Huygens sen. The 
original Dutch MS. is at Leyden, and has recently been printed in Zwvr. 
Compl. de Chr. Huygens (1899), Vol. VIII, No. 2099, p. 21. 

* See p. 135 supra, 2nd observation on pepper-water: 24 May 1676. 

® Phil. Trans. (1677), Vol. XII, p. 829. 


To Oldenburg’s inquiries Leeuwenhoek sent the following 
characteristic reply’: 
Your very welcome letters of the 12th and 22nd 
ultimo” have reached me safely. I was glad to see that 
Mr. Boyle* and Mr. Grew* sent me their remembrances : 
please give these gentlemen, on my behalf, my most 
respectful greetings. “T'was also a pleasure to me to see 
that the other Philosophers’ liked my observations on 
water, etc., though they found it hard to conceive of the 
huge number of little animals present in even a single 

"Letter 19. 23 March 1677. MS.Roy.Soc.—The greater part of this 
letter was translated into English and published in Phil. Trans. (1677), 
Vol. XII, No. 134, pp. 844-846. The original MS., in Dutch, is accompanied 
by a MS. translation into Latin, concerning which L. makes the following 
statement in a postscript (in Dutch, which I translate): “ Sir, seeing that 
you are most times hard pressed to find time to translate my observations 
into the English tongue, and mentioning this to a gentleman who hath 
divers times been to visit me; this gentleman offered me his services, to 
translate into Latin such of my observations as I may perchance com- 
municate to you: which offer I did not decline, and I now send you his 
Latin copy herewith, along with my own letter. I await your answer, and 
would know if I can serve you by acting in this way in future.” Although 
Oldenburg’s translation is said to be “ English’d out of Dutch’, it appears 
to me almost certain—from comparison of the three versions—that the 
English was really rendered from the Latin, and not from the Dutch copy. 
My own translation—above—is from the latter, written in L.’s own hand. 
This will explain several slight discrepancies between Oldenburg’s version 
and mine. It must be added that L. himself also printed a considerable 
extract from this letter, at a later date, in his Letter 96 (9 Nov. 1695)— 
published in the Dutch and Latin works. 

*7.e., February 1677. 

*The Hon. Robert Boyle (1627-1691)—“ Father of Chemistry and 
brother of the Earl of Cork.” 

“Nehemiah Grew (1641-1712), to whom several of L.’s most interesting 
letters were addressed, was a Doctor of Medicine (Leyden, 1671) and 
Secretary of the Royal Society from 1677 to 1679. He was educated at 
Pembroke Hall, Cambridge, and became a Fellow of the Society in 1671: 
but he is best known for his botanical work, and his catalogue of the 
Society's museum. As a botanist he was the rival of Malpighi, and a 
pioneer in the study of vegetable morphology. His later work is deeply 
tinctured with religion. (His father, Obadiah Grew, was an ejected 
minister of the English Church.) For his biography see the Dict. Nat. 
Biogr. and Arber (1913). 

*de Heeren Philosophen MS.—i.e., the Fellows of the Royal Society. 

LETTER 19. 23 mMARCH 1677 169 

drop of water. Yet I can’t wonder at it, since ’tis 
difficult to comprehend such things without getting a 
sight of ’em. 

But I have never affirmed, that the animals in water 
were present in such-and-such a number: I always say, 
that I imagine I see so many. 

My division of the water, and my counting of the 
animalcules, are done after this fashion. I suppose that 
a drop of water doth equal a green pea in bigness;* and 
I take a very small quantity of water, which I cause to 
take on a round figure, of very near the same size as a 
millet-seed. ‘This latter quantity of water I figure to 
myself to be the one-hundredth part of the foresaid drop : 

4s for I reckon that if the diameter of a millet-seed 

45° be taken as 1, then the diameter of a green 

225 -pea must be quite 43. This being so, then a 
_— + quantity of water of the bigness of a millet-seed 
20m”, maketh very nearly the sz part of a drop, ac- 
cording to the received rules of mathematicks 

00 ©. (8.-« Shown. in the margin). This amount of 
~ 91] Bas water, as big as a millet-seed, I introduce into 

a clean little glass tube (whenever I wish to 
equalone let some curious person or other look at it). 
Sie This slender little glass tube, containing the 
(vobmme)- “water, I divide again into 25 or 30, or more, 
parts; and I then bring it before my microscope, by 
means of two silver or copper springs, which I have 
attached thereto for this purpose, so as to be able to 
place the little glass tube before my microscope in any 
desired position, and to be able to push it up or down 
according as I think fit. 

I showed the foresaid animalcules to a certain 
Gentleman, among others, in the manner just described ; 
and he judged that he saw, in the zoth part of a quantity 

'In Letter 96, L. tells us that his standard “ green pea”’ weighed 8 grains. 
See p. 214 infra. 



of water as big as a millet-seed, more than 1000 living 
creatures. This same Gentleman beheld this sight with 
ereat wonder, and all the more because I told him that 
in this very water there were yet 2 or 3 sorts of even 
much smaller creatures that were not revealed to his 
eyes, but which I could see by means of other glasses 
and a different method (which I keep for myself alone). 
Now supposing that this Gentleman really saw 1000 
animalcules in a particle of water but soth of the bigness 

of a millet-seed, that would be 30000 living 
Shoe creatures in a quantity of water as big as a 
9730000 +4+%millet-seed, and consequently 2730000 living 

creatures in one drop of water. Otherwise, I 
imagine the quantity of water to be of the bigness of a 
coarse sand-grain; and in this quantity I imagine that 
I see upwards of 1000 living creatures. Now I take it 
that the bigness of a coarse grain of sand beareth the 
following proportion to a drop of water: If the diameter 
of a sand-grain be 1, then that of a drop of water is more 
than 10, and consequently a drop of water is more than 
1000 times bigger than a sand-erain. ‘Thus there are 
more than a thousand times a thousand living creatures 
in a drop of water. Tis in such a fashion that I make 
my uncertain and imaginary reckoning of the animalcules 
in water: but I guard myself, so far as ‘tis possible, 
against making the number too big, as you can see from 
the foregoing lines of my letter, wherein I have made 
the number not half so big as others well might do. 

My counting is always as uncertain as that of folks 
who, when they see a big flock of sheep being driven, 
say, by merely casting their eye upon them, how many 
sheep there be in the whole flock. In order to do this 
with the greatest exactness, you have to imagine that the 
sheep are running alongside one another, so that the flock 
has a breadth of a certain number: then you multiply 
this by the number which you likewise imagine to make 
up the length, and so you estimate the size of the whole 


flock of sheep. And just as the supposed number may 
differ from the true number by fully 100, 150, or even 200, 
in a flock of 600 sheep, so may I be even more out of my 
reckoning in the case of these very little animalcules: for 
the smallest sort of animalcules,’ which come daily to my 
view, I conceive to be more than 25 times smaller than 
one of those blood-globules which make the blood red 5 
because I judge that if I take the diameter of one of 
these small animalcules as 1, then the diameter of a 
blood-globule is at least 3. 

These, Sir, are the trifling observations which I have 
shown to divers curious persons, to their great satisfaction ; 
but the other things that I have seen, and my particular 
microscope, I cannot yet resolve to make public: which 
I beg you, Sir, and your fellow philosophers, not to take 

Since sending off my letter” concerning the little 
animals in water, I’ve not remained idle; but I have con- 
tinued to examine divers sorts of water, examining even 
that which was distilled or boiled. During the last sharp 
spell of cold, when all the little animals had perished, I let 
the water thaw by the fire; and when it had stood a whole 
day in my bedchamber, with the fire kindled all the time, I 
saw, after the lapse of 24 hours (and at another time after 
17 hours), that living creatures had come again in the 
water. Upon this subject I might, indeed, say something 
further; but I note that my former letter is still under 
your consideration, so I will spare you more. 

To give your Philosophers further assurance, con- 
cerning the reality of the multifarious living creatures in 
even only a very little quantity of water, ‘tis my intention, 
when they appear again in great plenty in the water, to 
obtain testimony thereof, which I shall then send you. 

The foregoing Letter was read at the meeting of the Royal 
Society on 5 April 1677 [O.S.]; and the observations excited 

‘7.e., Bacteria. 
? Referring to Letter 18 (p. 117 swpra). 


so much interest that the Secretary (Nehemiah Grew) was 
ordered to repeat Leeuwenhoek’s experiments, for the greater 
satisfaction of the Fellows.’ 

In a further communication on the same subject—and 
various others—Leeuwenhoek fulfilled his promise to send 
the testimony of divers credible eye-witnesses in support of the 
truth of his statements. To a modern worker it seems some- 
what curious that a scientific observer should think of calling 
in such people as notaries public and ministers of religion to 
vouch for the accuracy of his observations: but Leeuwenhoek 
could think of no better method of establishing his bona fides, 
and the result was, no doubt, satisfactory to all parties con- 
cerned. It should be remembered that Leeuwenhoek’s 
reputation was not yet firmly established at this early stage in 
his scientific career, and we know that certain people had 
already expressed their doubts as to the accuracy of his 
observations. Among them was Christiaan Huygens, who, 
writing to Oldenburg in 1675, says: “I should greatly like to 
know how much credence our Mr Leeuwenhoek’s observations 
obtain among you. He resolves everything into little 
globules; but for my own part, after vainly trying to see some 
of the things which he sees, I much misdoubt me whether 
they be not illusions of his sight ; especially when he professes 
to discover the particles whereof water, wine, and other 
liquors, are composed.” It was this scepticism regarding 
his researches, apparently, which caused Leeuwenhoek to 
send those long and detailed extracts from his note-book— 
which, as already noted, are peculiar to his 18th Letter—to 
the Royal Society. The disbelievers, therefore, did a signal 
service to posterity; for they put Leeuwenhoek on his mettle, 

"Cf. Birch, Vol. III, p.338: “It was ordered, that Dr. Grew should be 
desired to try what he could observe in the like waters; and that for this 
purpose an extract should be given him by Mr. Oldenburg of Mr. 
Leewenhoeck’s observations formerly read to the Society.” 

* Huygens to Oldenburg ; 30 January 1675. MS.Roy.Soc. This letter 
has lately been published in (uur. Compl. de Chr. Huygens, Vol. VII, 
No. 2003, p.399. The original is in French, and the above is my 
translation of the passage in question—-Huygens was mistaken in 
supposing that L. laid claim to having detected the particles (molecules) 
of which water and other liquids consist—as is abundantly proved by L.’s 
own statements: see, for example, his letter to Const. Huygens (20 May 
1679) translated on p. 187 infra. 

LETTER 21. 5 OCTOBER 1677 iV (e: 

and thereby enabled us to read today a detailed record of some 
of the most remarkable and original researches ever executed. 

The further communication referred to above is 
Leeuwenhoek’s 21st Letter—according to my reckoning— 
and the passages in question are as follows’: 

In my letter of 23 March, 1677, I demonstrated that 
one drop of water (which is as big as a green pea) is 
equal in volume to 92%” millet-seeds: and to bring it 
home to some friends of mine who could not grasp this, 
I took 6 millet-seeds and stuck them alongside one 
another with a little pitch. Then, with a pair of callipers, 
I took the width of the axes of the said millet *-seeds, and 
found the distance between the points was equal to the 
axis of a big currant; and I remarked that the cube of 6 
is 216. Now, said I, let us put an uncertain for a certain 
quantity; and let us say, that as the currant sinks in 
water, and the millet-seeds sink likewise in water, they 
are therefore of like gravity: this being so, then 216 
millet-seeds should weigh as heavy as this currant. I 
then placed the currant in a small but exceeding nice 
pair of scales, and found that 212 millet-seeds were of 
equal weight with the currant. 

I said also* that when I should again have a great 
number of living creatures in water, I would send you 
testimonials thereof, for the satisfaction of yourself and 
the other Philosophers: these I now send you herewith, 
from eight several Gentlemen, some of whom say that 


"From Letter 21. 5 October 1677. To Oldenburg. MS.Roy.Soe. 
An English abstract was published by R. Hooke in his Lectures and 
Collections (1678), Part II; Letter I, pp. 81-83. (Also reprinted in Hooke’s 
Lectiones Cutlerianae, 1679.) Apparently this letter, though sent to 
Oldenburg, came into Hooke’s hands when he succeeded him—after his 
death—as Secretary of the Society.—This letter is called “ [26] Brief 18B”’ 
by Vandevelde (1922, p.356), who, as he was unaware of the existence of 
the original MS., could assign no date to it. My translation is made from 
the manuscript itself. 

? This is a mistake. It should be 91 (91°125). See p. 169 supra. 
® In the MS. the word geerst (= millet) is here miswritten “ geest’’. 
* 7.e., in his letter of 23 March 1677. See p. 171 supra. 


they have seen 10,000 living creatures in a parcel of 
water the bigness of a millet-seed, while others say 
80,000 and also 45,000. I have generally counselled 
these Gentlemen, when giving their testimony, to put 
down but half the number that they judged they had 
seen; for the reason that the number of animalcules in 
so small a quantity of water would else be so big, that 
’twould not be credited: and when I stated in my letter 
of 9 October, 1676, that there were upwards of 1,000,000 
living creatures in one drop of pepper-water, I might with 
truth have put the number at eight times as many. For 
if there be, as the testimonial saith, 45,000 animalcules in 
a quantity of water as big as a millet-seed, then 
3? there would be 4,140,000 living creatures in a 
50000 Crop of water: and over and above this vast 
4050000 number, I cau say that I am able to discern at 
4140000 times even as many other living creatures, which 
are so little that they were hid from the sight 
of the Gentlemen who gave their testimony. ‘The first 
number, when doubled, amounts therefore to 8,280,000 
living creatures in one drop of water. This is incon- 
ceivable: but let us put it thus, that supposing a coarse 
grain of sand be divided into 8,000,000 parts, then I do 
indeed see little living creatures in water which are no 
bigger than these particles of sand would be. And this 
being conceived, ’twill not appear so marvellous. 

The attestations' of the eight eye-witnesses have for- 
tunately been preserved with the foregoing letter. There are 
actually five of them, but one bears three signatures and 
another two—making eight testimonies in all. One® is in 

1 Presented at a meeting of the Society on 15 October 1677, and read on 
November 1 [0.8.]. Cf. Birch, Vol. III, pp. 346, 347. 

? By Alexander Petrie, son of a more famous father of the same name 
(ca.1594-1662) who was a Scottish divine and minister of the Scottish 
church at Rotterdam. The father’s life will be found in Dict. Nat. Biogr., 
but I have been unable to discover anything further about the son—the 
present writer. 


English, and is written and signed by the minister of the 
English church at Delft. It is as follows’: 

I underwritten, being willing to give testimony unto 
that whereof I was an eye-witnesse, do declare that having 
seen and read Mr Leewenhoecks letter of March 23. 1677. 
as it is set down in the printed Philosophical Transactions, 
Numb. 134. p. 844. I was desirous to see a proof of 
what I found there related; and for my satisfaction, Mr 
Leewenhoeck did put a litle quantity of water, about the 
bignesse of a Millet-grain, into a very slender glasse-pipe, 
on which looking through his Microscope, I did see a 
very great number of litle animals moving in that water, 
so many that I could not possibly number them, and to 
my sight they seemed to exceed the number expressed in 
his fore-mentioned letter: and moreover, being desirous 
to see a proof whether those animalcula were indeed 
living animals, Mr Leewenhoeck by adding a very small 
quantity of vinegar to the same water, and putting it 
again into the same glasse-pipe, I did see those litle 
animals in the water, but they did not moove at all (being 
killed by the vinegar) which I beheld with admiration, 
that in so small a quantity of water I should see such a 
vast number of those litle animals. Whereof, being 
Testis oculatus, I was willing at the desire of ingenious 
Mr Leewenhoeck to confirm the truth of his relation by 
this testimony written and subscribed by me, in Delft, 
Aug: =a HORT: 
Alex: Petrie. 
Pastor of the English Congregation in Delft. 

The other testimonials are couched in similar terms. There 
is a long one in Latin, signed by “ Benedictus Haan’ Pastor 

* MS. Roy. Soe. 

2 Benedictus Haan (sew de Haan) was Lutheran minister successively at 
Breda (1666), Delft (1675), and Amsterdam (1692). He died in 1702, and 
is otherwise dimly remembered as the author of sundry verses which, 
according to van der Aa, afford very feeble proof of his ability as a poet.” 



Luther: Delph:” and ‘ M. Henricus Cordes’ Past. Luth. 
Hag.’ ; and there are two shorter ones in the same language 
signed respectively by “ R. Gordon’ Medicinae Studiosus”’ and 
the three following persons: “J. Boogert* J.U.L. et Notar. 
Publ.” ; ‘“ Rob. Poitevin * Doct. m. monspel.” ; ‘“‘ W. V. Burch ° 
J.U.L. et coram curia Hollandiae advt.” The remaining 
attestation is short and in Dutch, and is signed ‘“ Aldert 

* Hendrik Cordes, Lutheran minister at The Hague from 1674 to 1678, 
was the son of Paulus Cordes (1613-1674), who held a like office at 
Amsterdam. Hendrik, who died in 1678, is known to students of Spinoza: 
for his successor was the Colerus (Kéhler) who wrote the life of the Jewish 
philosopher. Colerus (1705), speaking of Spinoza, says: “He had a great 
esteem for Dr. Cordes, my Predecessor; who was a learned and good 
natured Man, and of an exemplary Life, which gave occasion to Spinosa 
to praise him very often. Nay, he went sometimes to hear him preach, 
and he esteem’d particularly his learned way of explaining the Scripture, 
and the solid applications he made of it. He advised at the same time his 
Landlord and the People of the House, not to miss any Sermon of so 
excellent a Preacher.” See Pollock (1899) p. 395. 

*This was Sir Robert Gordon (1647-1704), who “travelled much into 
foreign countries for his improvement, was a man of extensive learning and 
knowledge, and particularly skilled in mechanics and chemistry.’’ He was 
son of Sir Ludoyick Gordon, of Gordonstoun, Elginshire, and became a 
Fellow of the Royal Society in 1686. (Cf. Birch, Vol. IV, pp. 454, 455.) 
Owing to his scientific pursuits he became known in the neighbourhood 
where he lived as “ Sir Robert the Warlock”. For his life see the Dict. 
Nat. Biogr. 

*J. Boogert. The letters J.U.L. stand for Juris Utriusque Licentiatus— 
a degree inferior to that of Doctor. It is evident, therefore, that he was a 
lawyer and notary public; and Mr Bouricius tells me further that his 
forename was Johannes and he was the son of a physician. It is probable 
that he was the Jan Fransz. Boogert (or Bogaert) mentioned in Boitet 
(1729, pp. 453, 495) as one of the governors of the reformatory at Delft in 
1677, and a governor of the poor-house in 1680. This J. B. died in 1702. 

‘Robert Poitevin, Doct[or] m[edicinae] Monspell[liensis], I cannot 
trace further: but I find that several other medical men with the same 
surname also qualified at Montpellier, where other members of this family 
resided. Perhaps he was the Leeuwenhoeks’ family physician. Astruc 
(1767) makes no reference to him. 

°W. vlan der] Burch. The words following his name show that he 
was a barrister; and I think he must have been the Willem Reyersz. v. d. 
Burch (1627-1712), sometime town-councillor and “ weesmeester”’ at Delft, 
who is referred to in Boitet (1729, p.90 et alibi)—though Mr Bouricius 
(in litt.) considers this doubtful. 

*Aldert Hodenpijl. Mr Bouricius informs me that he was married to 


All these attestations bear out what Leeuwenhoek himself 
tells us in his letters. But they also tell us that the capillary 
glass tube containing the animalcules was as thick as a horse- 
hair * (Haan and Cordes), and that it was divided into a large 
number of measured parts, though it contained but a droplet 
of water no bigger than a millet-seed. Hodenpijl says the 
animalcules looked to him as large as lice, or even larger’: 
while Haan and Cordes declare that some of them appeared 
as big as bugs." 

To the testimony of these worthy men we may now add 
that of Christiaan Huygens, who, at the end of his French 
version of Leeuwenhoek’s observations,’ added the following 
remarks of his own’: “These are the observations of Mr. 
Leeuwenhoek. His manner of making them is to introduce 
the water into very little glass tubes, one third or one quarter 
of a line in diameter; and these he afterwards applies to his 
microscopes. He showed me some of these little insects very 
distinctly, continually tumbling about in the water”. We 
may suppose, accordingly, that Huygens, when he wrote this, 
had overcome his original scepticism regarding Leeuwenhoek’s 
observations. Indeed, the demonstration of which he here 
speaks was probably the stimulus which prompted him, soon 

Judith le Roy, and he has found records of the baptism of three of their 
children (circiter 1668): but he has been able to find out nothing of present 
interest about him in the Archives of Delft. It seems probable, however, 
that Aldert H. is identical with Aalbert H. who is recorded in Boitet (1729, 
pp. 519-20) as having been schutterkoning (= champion shot) of Delft in 
1661, 1665, and 1668. (The discrepancy between ‘‘ Aldert ”’ and “ Aalbert” 
may be easily accounted for—Mr Bouricius assures me—by the “ general 
slovenliness [slordigheid] in writing names at that time”.) Why L. sent 
his testimony I do not know—unless it was because his pre-eminence in 
shooting guaranteed the excellence of his eyesight. 

‘ad crassitiem pili equini crasso MS. 

* Haan and Cordes say 50 parts, Hodenpijl says 70, and Boogert and his 
co-signatories say 90. No doubt the discrepancy is to be explained by the 
circumstance that they recorded L.’s procedure on three different occasions. 

* hebbende de groote van een luijs, en sommige grooter MS. 

*apparebant ad magnitudinem cinvicis MS. 

> See p. 115, note 6. 

° Published in Guvr. Compl. de Chr. Huygens, Vol. VIII, p. 27. These 

remarks remained in manuscript until 1899, when this volume was published. 
The original is in French, and the above is my translation. 



afterwards, to make his own remarkable contributions to 

It cannot be doubted that the “ very smallest animalcules,”’ 

of which Leeuwenhoek himself speaks, were in reality not 
protozoa but bacteria. The particulars which he records prove 
this conclusively, and it is hardly necessary to make infusions 
of pepper—as I have done*—to convince oneself of this: 
while the fact becomes superabundantly clear from Leeuwen- 
hoek’s next letter on this subject, which was written at the 
beginning of 1678 and contains the following remarkable 
passage *: 

I can't help mentioning that I can now make out, very 
plain and clear, the shape of those little animals of the 
smallest sort, whereof I said before* that I could ascribe 
no figure to them ; and this because of the pleasure that 
I do take in their manifold delightful structures, and the 
motions that they make from time to time in the water. 
Upon the 4th of this present month,’ when it froze hard, 
I did fill a small clean glass with pounded pepper to 3 of 
its height, adding § of rain-water, and set it for the first 
night in my bedchamber. The next day, it’ being well 
softened, I put it’ in my closet; and within thrice 24 

" See p. 163 supra. 

? Cf. also Beijerinck (1913). 

* From Letter 23,14 January 1678. This letter was written to Robert 
Hooke, who published an incomplete English version of it in his Lectures 
and Collections (1678), Part II; Letter 2, pp. 84-89. This translation was 
made by Hooke himself: for in a letter to L., dated 10 March 1682 (MS. 
unpublished), he says so, and adds: “I have as neere as I could followed 
the sense of your Expressions though not verbatim.’’—I translate from the 
original MS. I may add that this letter serves to confirm my numeration 
of L.’s early epistles: for it is No. 23 according to my reckoning, and L. 
himself refers to it in his 113th Letter as “my 23rd”. It was read at a 
meeting of the Society on 24 Jan. 1678 (cf. Birch, III, 380), but is not to be 
found in the Phil. Trans., nor in the Dutch or Latin editions of the letters. 
Hooke reprinted his translation in Lectiones Cutlerianae, Part V (1679). 

* Letter 18. (Seep. 143 supra.) The organisms referred to were evidently 

° January, 1678. 

® ¢.e., the pepper. 

” i.e., the glass. 

LETTER 23. 14 JANUARY 1678 179 

hours I discovered in it’ so great a many of such incon- 
ceivably small creatures, that a man’s mind may not 
contain them all: and in my judgement, the sort that 
were most plentiful were much more than 1000 times 
thinner than a hair of one’s head, and 3 or 4 times as 
long as thick. These would oft-times shoot so swiftly 
forward with the hindmost part of their body, that you 
might think you saw a pike darting through the water ; 
yet each shoot was, in length, most-times about half a 
hair’s breadth. ‘The figures of the other sorts of creatures, 
whereof some were even less, I shall pass over, else 
’twould take all too long a-writing: I will only say, that 
in pepper-water, that hath stood somewhat long, I have 
oft-times seen, among the extraordinary little animalcules, 
little eels;? and the structure and the motions which 
these had, was as perfect as in big eels. But they were, 
to my eye, quite a thousand times thinner than a hair off 
one’s head ; and if a hundred of these little eels were laid 
out end to end, the whole length of them would not reach 
to the length of a full-grown one of those eels that are in 
Leeuwenhoek’s next letter in which we find any mention 
of protozoa was written in September of the same year (1678). 
It also contains some observations of whose precise signifi- 
cance I am uncertain: but it is so characteristic, and so 
clearly reveals his method of working and ways of thinking, 
that I cannot refrain from quoting it. This is what he there 

’ i.e., the pepper-infusion in the glass. 

* Spirilla. 

® Anguillula aceti—the “ vinegar-eel’’—which L. regarded as really a 
little fish. Large specimens measure about 1:5 mm. in length: ef. 
p. 335 infra. 

“ From Letter 26. 27 September 1678. To Nehemiah Grew. MS.Roy.Soc. 
Unpublished. (A poor contemporary English MS. translation accompanies 
the original Dutch MS.) The above is my translation of a part of the 
letter.—There is an important reference to this epistle in L.’s letters to 
Magliabechi (vide Targioni-Tozzetti, 1745: Epist.I, Vol. II, p. 345); but 
the observations on the reddening of grass are there referred to the year 
1648—which must assuredly be a misreading or misprint for 1678. 




But many of the things we imagine, and the natural 
objects that we inquire into, are very insignificant ; and 
especially so, when we see those little living animals 
whose paws we can distinguish, and estimate that they 
are more than ten thousand times thinner than a hair of 
our beard; but I see, besides these, other living animal- 
cules which are yet more than a hundred times less, and 
on which I can make out no paws, though from their 
structure and the motion of their body I am persuaded 
that they too are furnished with paws withal: and if 
their paws be proportioned to their body, like those of the 
bigger creatures, upon which I can see the paws, then, 
taking their measure at but a hundred times less, it 
follows that a million of their paws together make up but 
the thickness of a hair of my beard; while these paws, 
besides their organs for motion, must also be furnished 
with vessels whereby nourishment must pass through 

Because many people, both in the towns and in the 
open country, are stricken with fever,’ and because their 
shoes get very red whenever they walk through the grass 
in the meadows; the common man concludes that the air 
is therefore infected, and very fiery. This coming to my 
ears, I betook myself without the town and examined the 
dew: but I could find nought in it worthy of remark. 
However, seeing that my shoes also had got reddened by 
the grass, I turned my attention to the grass itself, and 
saw that some of it was studded with reddish dots. 
Bringing these before my microscope, 1 saw that they 
consisted of small globules, whereof upwards of a thousand 
did not equal the bigness of a small sand-grain. (I find 
there are various kinds of grass: and among others, one 
sort that was very rough, which was not contaminated °*.) 
Inquiring after a reason for these globules being upon the 

’ Probably a reference to malaria, and therefore of some interest at the 

present time. 

> Marginal note in original. 

LETTER 26. 27 SEPTEMBER 1678 181 

grass, I observed that they came not out of the air (as 
was the vulgar opinion), but out of the grass itself: the 
cause whereof I conceived to be this. The dry cold, that 
we had some three weeks earlier, caused the death of the 
extreme tips of some blades of grass; and this was followed 
by very warm weather, which drove fresh nourishment 
again upwards through the pores’ in the grass. But this 
food-matter, wherewith the pores of the grass were filled, 
being unable to get out at the top (because the ends or 
the uppermost pores of the grass were stiff and dried up), 
burst open the pores in many places where they were 
most weakened ; and thus many globules were squeezed 
out of them. These globules, lying stuck together upon 
the outside of the grass, and becoming stiffer on exposure 
to the surrounding air, took upon themselves a reddish 
colour; whereas these same globules, when they le in- 
closed in the pores, are green.” And whenever one 
happens to strike one’s foot against such grass, the said 
globules are dusted off it, and make one’s shoes reddish. 
But since a red colour is most agreeable with the notion 
of fire, we must not take it amiss in the common man if 
he deems the said substance to be a fiery matter: seeing 
that there are among us physicians (who fancy themselves 
experienced) who say, when they see blood whose whey- 
like matter * is yellow, that the blood is bilious; or say of 
black blood, that ’tis burnt: just as if everything yellow 
were bile; and everything black, burnt.’ 

Meantime the Fellows of the Royal Society’ had not been 
wholly idle in the matter of the “little animals.” Robert 

* Port MS. 

> L. evidently confused the red corpuscles on the grass-blades with 
chloroplasts within them. 

* i.e, serum. 

* It is clear from this, and many another passage in L.’s writings, that 
he had but a poor opinion of the general medical practitioner of his day. 

*> The Fellows (or some of them) would perhaps have taken particular 
interest in the observations on infusions: for they would recall—unlike 



Hooke, who succeeded Oldenburg in 1677 as Secretary, 
himself repeated the experiments with pepper-water and other 
infusions. In 1678 he published’ some account of his obser- 
vations, which confirmed Leeuwenhoek’s findings: and his 
experiments were also briefly communicated to Leeuwenhoek 
by letter at the end of 1677. Hooke’s published description 
records that he succeeded in seeing the animalcules—-or some 
like them—described by Leeuwenhoek: “some of these,” he 
says, “so exceeding small, that millions of millions might be 
contained in one drop of water.”* A draft of Hooke’s unpub- 
lished letter is still in possession of the Royal Society; and as 
it contains several points of interest J will now give it. He 
wrote °: 

The papers you directed to the Lord Brouncker* were 
read at a full meeting of the Royall Society and very 
kindly accepted by the Members thereof and they have 
orderd me to returne you both their thanks for soe freely 
communicating your observations, and also an account 
of what hath been here done in order to verify your 
observation concerning the small animalls you have first 
discovered in Pepper-water. 

Having steeped then in Raine water pepper wheat 

most modern Fellows—that Bacon, whose writings had so profound an 
influence upon the Society at its inception, had emphasized the need of 
inquiry into the various substances which produce animalcules by putre- 
faction. Cf. Nov. Org., Lib. II, cap.50: “Etiam materiae diversae putre- 
factionum, unde animalcula generantur, notandae sunt.” 

* See Lectures and Collections made by Robert Hooke (1678). Part II, 
Microscopium. Also reprinted in Lectiones Cutlerianae (1679). 

* Ibid., p.83. Hooke evidently refers to bacteria—not protozoa. 

* MS. letter (unpublished)—R. Hooke to Leeuwenhoek, Dec. 1 [?— date 
partly obliterated], 1677. Roy.Soc.MSS. The original is in English, and 
I give it exactly as written—only omitting a part at the end which has no 
bearing upon the subject under consideration. I have merely expanded 
words which are contracted in the original—for the reader's convenience, 
and for typographical reasons. The letter is in Hooke’s own hand, and is 
signed “ your very great admirer and honorer R.H.” 

* William, second Viscount Brouncker (1620 ?—1684)—an Irish peer. 
He was M.D. (Oxford) and a mathematician, and an original Fellow and 
first President of the Royal Society on its re-foundation in 1662-3. 


barly oats pease and several other graines,' and having 
fitted up some microscopes which had layne a long 
while neglected, I having been by other urgent occupa- 
tions diverted from making further inquirys with that 
Instrument, I began to examine all those severall Liquors 
and though I could discover divers very small creatures 
swimming up and down in every one of those steepings 
and even in Raine it self and that they had various 
shapes & differing motions, yet I found none soe ex- 
ceedingly filled and stuffed as it were with them as was 
the water in which some cornes of pepper had been 
steeped. Of this the President & all the members 
present were satisfyed & it seems very wonderfull that 
there should be such an infinite number of animalls in 
soe imperceptible a quantity of matter. That these 
animalls should be soe perfectly shaped & indeed with 
such curious organs of motion as to be able to move 
nimbly, to turne, stay, accelerate & retard their progresse 
at pleasure. and it was not less surprising to find that 
these were gygantick monsters in comparison of a lesser 
sort which almost filled the water. 

It seems clear that the ‘“gygantick monsters’’ were 
protozoa, while those of the “lesser sort” were bacteria. The 
foregoing lines contain, I believe, the first mention of the 
discovery of any of these organisms in infusions of wheat, 
barley, oats, and peas: for none of these are recorded by 
Leeuwenhoek as having been used in making the “ steepings 4 
employed in his own experiments. It is therefore unfortunate 
that Hooke—so far as I can ascertain—never wrote any 
further descriptions of the organisms which he discovered. 

Rumours of these remarkable discoveries spread, it would 
appear, into even the highest circles : for in another letter from 
Hooke to Leeuwenhoek, written a little later, the following 
passage occurs *: 

1 At a slightly later date—at a meeting of the Society on 7 March 
1678—Hooke also demonstrated the presence of “ animalcules ” in infusions 
of aniseeds and coffee. See Birch, Vol. TEE paso. 

2 MS. letter (unpublished), R. Hooke to Leeuwenhoek, dated 18 April 


The prospect of those small animalls have given great 
satisfaction to all Persons that have viewed them. His 
majesty * having been acquainted with it, was desirous to 
see them and very well pleasd with the Observation and 
mentiond your Name at the same time. I know not 
whether any of the ways I have here made use of for the 
Discovery of them may be in any thing like those with 
which you make your observations. But I have two or 3 
other ways which I shall shortly communicate,’ that doe 
farr exceed those I have here mentiond.’ 

Some important additional particulars regarding Hooke’s 
observations can be gathered from Birch’s History. He tells 
us* that at the meeting of the Society held on 1 November 
1677 O58), 

There were produced a great many exceedingly small and 
thin pipes of glass of various sizes, some ten times as big 
as the hair of aman’s head; others ten times less. These 
were made, in order to try a conjecture of Mr. Hooke 
propounded to the Society, that the discoveries, affirmed 
to be made by Mr. Leewenhoeck, were made by help of 

1678 (Roy. Soc. MSS.). The original, of which only a part is here copied, 
is in English. It is written in Hooke’s hand and signed “R.H.”’ I again 
expand the abbreviations in the original, for the reader's convenience. 

1 j.e., King Charles II of England, “ Founder” and Patron (Fundator et 
Patronus) of the Royal Society—as he is styled in the Charta secunda of 

2 The communication will be found in Hooke’s Lect. & Collect. (1678), 
p. 89 et seqq. 

* This letter from Hooke is referred to by L. at the end of his own 
Letter 28, 25 April 1679, to N. Grew (Brieven I, p.13: first published in 
Dutch in 1686). As the 28th Letter deals largely with spermatozoa, it has 
often been erroneously inferred that Hooke demonstrated spermatozoa—not 
protozoa—to the King. But the correspondence between Hooke and L. 
affords no grounds for such an inference; and I have been unable to 
discover any evidence in support of the accepted belief that the Merry 
Monarch was once entertained at an exhibition of spermatozoa by the 
Royal Society (or any member thereof). This myth probably originated 
with Haller (Elementa [1765], VII, 523)—as Cole (1930, p. 14) has already 

* Birch, Vol. III, p. 346. 


viewing with a good microscope such small pipes contain- 
ing the liquor or water, in which those multitudes of 
exceedingly small insects or animals wriggling among 
each other are discovered; for that he alledged, that the 
said pipes being filled with liquors became themselves as 
it were magnifying glasses. . . . . . It was therefore 
ordered, that against the next meeting pepper-water should 
be provided, and some better microscope than that made 
use of, that the truth of Mr. Leewenhoeck’s assertions 
might, if possible, be experimentally examined. 

Accordingly, at the next meeting, on 8 November 1677, 
“the first thing exhibited was the experiment charged on 
Mr. Hooke at the last meeting, of examining pepper-water with 
better microscopes and thinner and small pipes.”* But the 
experiment was not wholly satisfactory, and various objections 
to the observations were raised by the Fellows present. At 
the following meeting, however, on November 15, ample 
confirmation was forthcoming. In the words of Birch :* 

The first experiment there exhibited was the pepper- 
water, which had been made with rain-water and a small 
quantity of common black pepper put whole into it about 
nine or ten days before. In this Mr. Hooke had all the 
week discovered great numbers of exceedingly small 
animals swimming to and fro. They appeared of the 
bigness of a mite through a glass, that magnified about 
an hundred thousand. times in bulk; and consequently it 
was judged, that they were near an hundred thousand 
times less than a mite. Their shape was to appearance 
like a very small clear bubble of an oval or egg form; 
and the biggest end of this egg-lke bubble moved fore- 
most. They were observed to have all manner of motions 
to and fro in the water; and by all, who saw them, they 
were verily believed to be animals; and that there could 
be no fallacy in the appearance. ‘They were seen by Mr. 

' Birch, Vol. III, p. 349. 
* Bireh, Vol: IL, p: 352. 


Henshaw, Sir Christopher Wren,’ Sir John Hoskyns,° 
Sir Jonas Moore,‘ Dr. Mapletoft,? Mr. Hill,® Dr. Croune," 
Dr. Grew,* Mr. Aubrey,’ and divers others; so that there 
was no longer any doubt of Mr. Leewenhoeck’s discovery. 

Leeuwenhoek’s next communication on the “ animalcules’’ 
in infusions was sent to Robert Hooke, and is very brief; but 
it was accompanied by a copy of a very curious and interesting 
letter which he had previously written to Constantijn 
Huygens. In the letter to Hooke he says: 

As I see and hear that you are a man much given to 
speculation, I have thought fit to send you a copy of a 
very rough calculation which I set down on paper at 
the urgent intreaty of Mr. Constantijn Huygens van 

1 Thomas Henshaw (1618-1700), barrister and author: Vice-President 
and an original Fellow of the Society. Cf. Dict. Nat. Biogr. 

* Christopher Wren (1632-1723), artist and famous architect—soon to be 
President of the Society (1680)—too famous to need further annotation. 

* John Hoskyns (1634-1705), barrister of the Middle Temple: later 
Secretary and President of the Society. Cf. Dict. Nat. Biogr. 

* Jonas Moore (1617-1679), mathematician and surveyor. Elected F.RB.S. 
in 1674. He is several times mentioned by Pepys in his Diary, and his life 
is given in the Dict. Nat. Biogr. 

* John Mapletoft (1631-1721), M.D. and D.D., of Trinity College, 
Cambridge. Elected F.R.S. in 1676. He was an intimate friend of John 
Locke, and before he became a divine practised medicine in London with 

* Abraham Hill (1635-1721), Treasurer of the Society, and an original 
Fellow. Commissioner of Trade in 1689—a business-man of no known 
scientific attainments. 

” See p. 48, note 2, supra. 

* See p. 168, note 4, supra. 

* John Aubrey [sew Awbrey] (1626-1697), the well-known antiquary ; an 
original Fellow of the Society. 

* From Letter 29a. 16 January 1680. MS.Roy.Soc. An English extract 
from this letter—and its enclosure—was published in Derham’s Philos. 
Expts. & Obss. of R. Hooke (1726), p. 55. (The letter is there incorrectly 
dated Jan. 6.) I translate from the Dutch original—A contemporary 
English MS. translation is preserved with the original Dutch MS. in the 
Roy. Soc. collection, but it has given me no help. The letter was read at 
the meeting of the Society on 22 Jan. 1680 [0.S.], and discussed at the 
following meeting on Jan. 29. See Birch, Vol. IV, p. 5. 


Zuylichem.* And I feel bound to say, furthermore, that 
last Friday evening I took some pepper-water, in which 
there were many living animalcules, and mixed it with 
about a like amount of rain-water, wherein I had put a 
quantity of pounded ginger: and forthwith examining 
this mixt water, I found that the animalcules were slow 
a-moving. Some hours afterwards, examining this water 
anew, I could perceive no animalcules whatsoever in it : 
but about twice 24 hours afterwards, I saw very distinctly 
some animalcules which I judged to be a hundred million 
times smaller than a sand-grain, but without being able 
to discern any of those animalcules that had been before 
in the pepper-water.” 

The enclosed letter to Constantijn Huygens, dated 20 May 
1679, I shall now give in full. The original, from which it 
was copied, is preserved among the Huygens manuscripts at 
Leyden *—the following being a complete translation of the 
copy sent to Hooke: 

Along with this goeth my calculation, which I confess 
is quite imperfect, seeing that my estimates were made 
by the eye alone. 

I have oft-times let my thoughts run on the extreme 
small vessels and sinews* wherewith the very little 

* The father of Christiaan Huygens the astronomer and mathematician— 
not his elder brother. Cf. p. 42, note 2, supra. 

* It is probable that the animalcules in the pepper-water were protozoa 
of some sort, which were killed when the ginger-water was poured upon 
them: while the very minute forms which developed in the mixture after 
48 hours were evidently a new crop of bacteria. 

* See Haaxman (1875), p. 136,—where the date is given as 21 May 
1679: but L.’s copy, sent to Hooke, is by himself dated May 20, as stated 
above. The copy was made with his own hand.—The original has recently 
been printed in full in Guvr. Compl. de Chr. Huygens, VIII, 168-172 (also 
there dated May 21). 

* Or “nerves”: MS. senwwen. Zenww nowadays means a nerve—as it 
often did to L.—but at an early date it also meant a sinew (tendon), and 
from what follows this seems to be the correct rendering here. (Cf. the 
original meaning of Lat. nervus and Gr. vedpov.) 




animalcules are furnished withal; and more especially 
when I have been asked, whether I am able to see the 
particles of water itself? T’o which I did often answer, 
that there be little animals in water that are many 
million times smaller than a sand-grain; and that these 
little animals, on which I can discern no feet, must not- 
withstanding be furnished with instruments for motion ; 
and that these instruments must themselves consist, in 
part, of blood-vessels which convey nourishment into 
them, and of sinews which move them; and that through 
these vessels, moreover, water must also pass. And this 
being so, we must suppose the particles of the water itself 
to be so small as to be, for us, inconceivable: and I’m 
persuaded that no man will ever advance so far in science 
as to be able to gaze upon the particles whereof water 
itself consisteth. 

I shall here first lay down the proportion which the © 
animalcules bear to a sand-grain, in so far as my eye is 
able to arrive at it; together with the number of 
animalcules proportionate to the bigness of a cubic 

I usually judge that three or four hundred of the 
smallest animalcules, laid out one against another, 
would reach to the length of the axis of a common grain 
of sand; and taking only the least number (to wit 300), 

27000000 animalcules together are 
as big as a sand-grain. 

Let’s assume that such a sand-grain is so big, that 
80 of them, lying one against the other, would make up 
the length of one inch as BC [Text-fig. 1]. 

LETTER TO CONST. HUYGENS. 20 may 1679 189 

80 sand-grains in the length of one 
80 inch. 

6400 sand-grains in a square inch. 

p 512000 sand-grains in a cubic inch. 
27000000 animalcules which make 
3 up the bigness of a 
(Text-Fic. 1.] sand-grain. 
amounting to 1382400000000 animalcules in a cube 
inch, as ABCDEF. 

This number of animalcules is so great, that if one had 
as many sand-grains, of the bigness aforesaid, then one 
could lade with them more than 108 of our ordinary sand- 
lighters; that is, reckoning one schagt of sand (which is 
144 cubic feet) to every lighter. 

I have let my thoughts run likewise on the very 
little vessels that are in our bodies, and have judged that 
they are above a thousand times thinner than a hair of 
one’s head; and I have therefore put the proportion of 
the very little vessels thus in relation to the body, in 
order to arrive afterwards at the proportion of the 
vessels in the little animals. 

First of all, I sought to know how many hairbreadths 
are equal to the length of one inch; and having by me a 
copper rule, whereon the inches are divided into 3 parts, 
and each of these again into 10 parts (thus altogether, an 
inch divided into 30 parts), I laid hairs from my periwig 
upon these divisions; and observing them thus through 
a microscope, I judged that 20 hairbreadths are equal to 
3a of an inch. Consequently, there are 600 hairbreadths 
in the length of one inch. 

Further, I measured, roughly, the thickness of my 
body above the hips, and judged (taking one thing with 
another) that the diameter of my body was 8 inches.’ 

‘ If this were approximately correct, then L. was considerably more 


Archimedes showeth that as 14 is to 11, so is the square 
of the diameter to the content of a circle.’ 

8 704 
64 14 507 square inches for my body’s thick- 
11 ness. 

600 _hairbreadths in a length of one inch. 
33 diameters of the very little vessels in 
our bodies for one hairbreadth (that 
is, reckoning the little vessels in our 
bodies 1089 times thinner than a 


gives 19800 little vessels in a length of one inch. 

gives 392040000 little vessels to a square inch. 
50 square inches for the body’s thickness 

gives 19602000000 vessels in the thickness of the body. 

If we now suppose that the little vessels bear the same 
proportion to the bodies of the little animals, as those in 
us do to our bodies; then, in order to compare the very 
little vessels of the animalcules with the thickness of a 
sand-grain, the number given above must still be multi- 
plied by 300 (since, as already said, a sand-grain is 300 
times thicker than an animalcule). 


slender than the apparently heavily-built man depicted in his portraits. 
Moreover, the statement is not easy to reconcile with the later record that 
at this date he weighed over 11 stone (ef. p. 222 infra). 

* Nowadays we usually find the area of a circle by 77°; but “/y X d’ is 
obviously the same thing, and Prof. D’Arcy Thompson informs me that it is 
actually in this form that the proposition is found in the Circuli Dimensio of 
Archimedes.—It is highly improbable, of course, that L. had ever studied 
the writings of this great mathematician. 


Consequently, if the thickness of 19602000000 

ar pe 300 
a sand-grain is 1, the vessels in cae A eee 
the little animalcules are 5880600000000 

And because this number is so exceeding great, I have 
thought good to express the proportion in terms of a 
hair’s breadth in relation to the circumference of the 

5400 miles’ for the length of the circumference 
2000 rods for every mile 

gives 10800000 rods for the circumference 
12 feet for one rod 

g1ves 129600000 feet for the circumference 
12 inches in one foot 

gives 1555200000 inches in the circumference 
600 hairbreadths in one inch 

gives 933120000000 hairbreadths for the length of the 


This number of hairbreadths, which is equal to the 
length of the circumference of the earth, even when again 
multiplied by 6 will not equal that number aforesaid 
which represents the proportion of the vessels in the little 
animals to the thickness of a sand-grain (as we have 
estimated it above). To sum up, then: 

As a sixth of a hair-breadth is: 

To a length of 5400 miles: 

So is one of the smallest vessels in the smallest 
animalcules : 

To the thickness of a sand-grain (of such size that 
80 thereof, lying one against another, equal a 
length of one inch). 

Sir, you have here the wonderful proportions that I 

‘ Leeuwenhoek’s ‘‘ mile’’, consisting of 2000 “rods” of 12 feet, is, as a 
simple calculation shows, equal to some 4% English miles. (The English 
mile = 320 rods, and the English rod = 162 feet.) 


conceive to exist in the secret parts of Nature: and from 
this appeareth also, that all we have yet discovered is but 
a trifle, in comparison of what still lies hid in the great 
treasury of Nature; and how small must be those particles 
of water’ which, to all appearance, pass many at a time 
through such tiny vessels. 

I hope that with this I have satisfied your require- 

I have given the foregoing letter in full for several reasons. 
In the first place, it serves to illustrate Leeuwenhoek’s fond- 
ness for simple mathematical deductions ; secondly, it shows 
very clearly that, in the case of his “smallest animalcules”’, he 
was dealing with bacteria; and thirdly, it shows the success 
and failure of the application of his “uniformitarian” principles 
to microscopic creatures. In his estimate of the size and 
numbers of the bacteria present in a minute drop of water, he 
was not mistaken: but when he proceeded to show, by simple 
arithmetic, the magnitude of the blood-vessels in such 
organisms, he went ludicrously astray. His education and 
his century both failed him. His greatness and his littleness 
are here revealed simultaneously—to those endowed with the 
accumulated knowledge of the next 250 years. Yet even at 
the present day Leeuwenhoek’s mistaken conclusion may 
serve as a warning to the biologist with statistical tendencies. 
It is surely worthy of remembrance, even now, that the most 
flawless mathematical calculations may sometimes be wholly 

Leeuwenhoek’s next observations on ‘‘animalcules” are 
contained in a further letter to Robert Hooke. After 
recording some observations of no* present interest, the letter 
ends thus: * 


" j.e., the molecules of which water itself is composed. 

> Referring to Const. Huygens’s request that he should put down on 
paper his calculations concerning the magnitude of the parts of the “little 
animals”’ (vide supra). 

° A few words which are perhaps not irrelevant to the present subject 
will be referred to later (see p. 207 infra). 

* Letter 30. 5 April 1680. To R. Hooke. MS.Roy.Soc. Published in 
Brieven, Vol. I (Dutch), and Opera Omnia, Vol.I (Latin): also an English 
abstract in Phil. Trans. (1693), Vol. XVII, No. 196, p. 593; but this does 
not include the passage here quoted. 

LETTER 30. 5 APRIL 1680 193 

In the court-yard of my house there stand two vines; 
and observing their growth to be such, that a moisture 
dripped from their shoots, I examined this sap on several 
successive occasions, just to see if I could discover any 
living creatures in it: and most times I discerned therein 
divers kinds of living animalcules, whereof one sort was 
uncommon big in comparison of the others; nay, I even 
saw some little animals that I had seen aforetime in 
divers sorts of water. Hereupon I repaired to my 
garden which lieth within this town, and there too I 
examined the sap dripping from the vines, but in it I could 
discover no living creatures, save only a little worm that 
was of an uncommon bigness,’ compared with the other 
animalcules. I betook myself thence to my garden which 
lieth without the town, and there again examined the sap 
from several vines, but could discover no living animalcules 
in it. I cut off pieces from two vine-branches, to make 
them drip the more, and went to examine the sap again 
next day, but could find therein nothing living. And 
I took a new glass phial, and caught the sap in it, and 
carried it home and examined it; but notwithstanding, 
I could perceive no living animalcules in it. I am 
now busy finding out, if ’tis possible, why there be living 
animalcules in one sap, but none in the other. 

A little later Leeuwenhoek addressed another letter on 
the same subject to Dr Gale,” and in it recorded the results 
of his further experiments and observations on the sap of vines. 
This letter is as follows: ° 

* Probably a nematode. 

* Thomas Gale (1635 ?—1702), a Doctor of Divinity, was at this time 
Secretary of the Royal Society—an office to which he was appointed in 
November, 1679. He was a Fellow of Trinity College, Cambridge, and 
Professor of Greek in the University from 1662 to 1672. Later (1697) he 
became Dean of York.—At the beginning of this letter L. says that he is 
writing to Gale because Hooke had informed him that Gale was become 
Foreign Secretary, and that he should therefore address his letters to him 
in future. 

° Letter 81. 13 May 1680. To Thomas Gale. MS.Roy.Soc. Printed 


This serves as a continuation of my letter of the 5th of 
April [1680], wherein I noted how I had observed living 
animalcules* in the sap leaking from the shoots of the 
vine standing in my court-yard; whereas in the sap 
which dripped from the vines in my garden, I could 
discover no living creature. I have divers times turned 
my thoughts to this matter, and can find no more 
satisfactory explanation thereof than the following : 

The rain-water, which is drawn aloft by the power of 
the sun, and forms the clouds, is commingled with the 
seed of these animalcules; and as it had been raining for 
several days running, before the date of my first observa- 
tions on vine-sap, the tags of leather, wherewith the 
branches of the vine were nailed fast against a stone 
wall, had become quite water-logged; but afterwards there 
followed a warm sunshine, which caused the vine-branches 
to drip, and thus the foresaid leathern tags were kept 
continually wet, by the dripping of the vine upon them; 
and in this manner not only did divers sorts of animals 
come forth from this rain-water, but they even (so I 
imagine) bred in it, and swam along the vine-branches, 
even to the topmost part of the vine, where the moisture 
dropped out. 

About 24 hours after I had dispatched my observations 
to Mr. Hooke, the vine-branches in my court-yard 
stopped dripping, and the weather grew uncommon warm, 
so that the vine-branches, and the leathers as well, got 
quite dry: hereafter, it rained near the whole night, then 
the sun shone in the morning, and it rained afresh in the 
afternoon: and observing that the leathern tags (with 
which, as remarked above, the branches of the vine were 
nailed fast to the wall) were once more soaked through, I 

in Brieven, Vol. I (Dutch), Opera Omnia, Vol. I (Latin), and briefly abstracted 

in English in Phil. Trans. (1693), Vol. XVII, No. 196, pp. 593-4,—along 

with the preceding letter. It was presented at a meeting of the Society on 

« 13 May 1680 [0.S.] (Birch, Vol. IV, p. 37). I translate the whole letter, 
with the exception of a few words at the beginning and the end. 

1 The MS. says Dierkens, but the printed letter has Dieren (=animals). 

LETTER 31. 138 may 1680 195 

examined the water that lay upon them, and in it I 
discovered! sundry little animals of the biggest sort 
previously seen in the sap aforesaid, and I saw some of 
a lesser sort lying dead: and when I examined these 
animalcules more narrowly, I found that they belonged to 
two kinds commonly present in ordinary waters.’ After 
this time, about the middle of April, it rained a whole day, 
and the night following ; and next morning, when the 
sun came out, I betook myself to my garden, and 
[examined]* the sap dripping froma vine-branch, which 
I had cut a few days before, in order to make it drip, at 
the same time tying or binding a strip of wash-leather 
around it, so that when it rained, the rain-water would 
stay caught in it, and not readily dry up, and thus get 
better mixed with the sap that dripped out: and in this 
water I discovered a few animalcules of the sort already 
described. I also examined the sap from a second vine, 
which I had likewise treated in the same way, and herein 
too I perceived the animalcules. I also visited a third 
vine, from which I had also previously cut off a branch, 
so that it would drip;* but this one I did not tie round 
with a leather, and I took the sap that ran down the 
branch at the place where it was most plentiful (namely, 
in a fork, where the shoot came off the stem); but I 

Aw «mA 
(Text-Fic. 2.] 
could perceive no living animalcules in it, though I saw in 
it, with admiration, many little chrysalises, or pupae, as 
in Fig. A A [see Text-fig. 2]: and although they were 

' gesien MS. ontdekt printed version. 

2 It is obviously impossible to identify these “animalcules”, though 
they were probably protozoa or bacteria of some sort. 

> A verb is here accidentally omitted from the MS. and also from the 
Dutch printed version. The sense evidently requires “examined” or 
“ observed’: and as the Latin translator supplied “ examinavi # do 
likewise. . 

4 These words (op dat die druipen soude) are in the printed version but not 
in the MS. 


more than a million times smaller than a coarse sand- 
grain, yet could I see very plainly that they were furnished 
with 5 joints. This appeared very strange to me, as I 
had formerly convinced myself that no water-animalcules 
proceed from such structures, and I had never conceived 
that animalcules of such littleness could live in the air. 
I took these chrysalises home, and put some of them in the 
air, to see what would come out of them; but within a 
few days, they got so dry that their former figure was 
scarce discernible ; and those which I meant to keep in 
water got lost. 

These trifles are all I have to tell you for the time 

The foregoing characteristic observations upon protozoa 
(or bacteria) show us an interesting picture of Leeuwenhoek 
at work—discovering new ‘‘animalcules” in new situations, 
wondering how they make their appearance and multiply in 
certain liquids, and endeavouring to account for their appar- 
ently erratic distribution. Soon afterwards he again attacked 
the problem of their generation, and sent the following account 
of his experiments : * 

When it became known to me that divers opinions 
have been expressed concerning the generation of little 
animals; and as I heard, especially, that a certain 
Gentleman’ hath writ that no living creature can be 
generated if the vessel, or bottle, in which any moisture 
or meat has been put, be tightly stoppered ; I had a mind 
to carry out some trials of this matter. 

* This sentence is in the MS. but not in the printed version. 

* From Letter 32. 14 June 1680. To Thomas Gale. MS.Roy.Soc. 
Printed in Brieven, Vol. I (Dutch) and Opera Omnia, Vol. II (Latin). No 
abstract of this letter was published in the Phil. Trans. though the letter is 
a very remarkable one. It contains, in addition to the observations here 
related, a description of yeasts obtained from beer—the first microscopic 
study of these organisms. 

* Doubtless Francesco Redi, whose celebrated treatise on “‘ the Genera- 
tion of Insects”’ first appeared in 1668. LL. could know of Redi’s work only 
by hearsay, since he was ignorant of Italian. 

eva Lan) 

ie ne; mint i 
aes mies: 
hin a Nhat: 
il “ul ih ‘ae 
uy Ms wt 

me LAr Ay 

a rat aoe 

bes re hah Naa haa 

I Se 
wn Ce ~ Nhneaia Mea wor aN nel ; 
ee Y aw Te), ; 
Aah, ‘eo iat ait) Nae ee se a 

Wh en hay yi Ha) od a py 

hi Se ey yi ia, ay es Wi, wine ia, ne 
oe mete, Slots oh 

we Ae , : 





ANNAN ass A 


illustrating the experiment with the pepper- 
tube. On the left, Leeuwenhoek’s original 
drawing (reduced to #): on the right, the same 
figure as improved by the engraver for re- 
production in the printed letter (same size). 

facing p. 197 

LETTER 82. 14 JuNE 1680 197 

Accordingly, I took two glass tubes, as ABCDEFHIKL 
[Plate XXIT], which, after they were both closed below at 
AL, were filled up to BK with pounded pepper, and then 
to CI with clean rain-water, as soon as it had been 
collected on May 26* in a clean china dish (in which no 
victuals had been put for quite ten years); then, by the 
heat of the flame, the glass was fashioned to the figure of 
ABCDGHIKL, having at its pointed end G a small 
opening ; for I considered that though the glass was now 
hot, the air within it would presently become equally cold 
with the air that was outside it; and after the lapse of 
about a quarter of an hour, I sealed up the aperture at G 
tight, by means of the flame. I also prepared myself a 
second glass, treating it likewise, save that in this I left 
the aperture at G open; in order to ascertain, if ’twere 
possible, in which water the living animalcules would first 
turn up. But after it had stood thus for three days, 
during which time I made divers observations upon it, I 
judged that if there were already any very little living 
animalcules in this water, ’twould not be possible for me 
to discover them, for the reason that the glass was too 
thick, and because of the many little particles of pepper 
which lay against the glass inside, so that it was not 
feasible to carry out such particular observations as the 
occasion required. On this account, I took a little water 
out of the second glass, through the small opening at G; 
and I discovered in it a great many very little animalcules, 
of divers sorts and moving about among one another, 
each several sort having its own particular motion. But 
as the first tube was of a somewhat thinner glass, I left it 
shut up till the fifth day, and during that time made 
various observations upon it; but I could discover no 
living animalcules in it, so I resolved to break the glass 
open at G, and in breaking it, the air which had thus 
been shut up for 5 days within it (and which was much 

" Anno 1680. 


compressed by the air-bubbles which rose everywhere to 
the top of the water) escaped with force out of the tube: 
for which reason I rather fancied that there would be no 
living creatures in this water. But I found the contrary: 
for no sooner did I draw some water through the small 
opening I had made at G, and bring it before my micro- 
scope, than I perceived in it a kind of living animalcules 
that were round, and bigger than the biggest sort that I 
have said were in the other water, though they were yet 
so small that it was not possible for me to discern them 
through the thickness of the glass tube.’ After this tube 
had stood thus open for 24 hours, I examined the water 
again ; and I then saw, besides the foresaid animalcules, 
various other sorts, though they were so small that they 
were hard to make out. 

Still, I bethought me that when that Gentleman afore- 
said spake of living creatures”, he meant only worms or 
maggots, which you commonly see in rotten meat, and 
which ordinarily proceed from the eggs of flies, and which 
are so big that we have no need of a good* microscope to 
descry * them. 

The whole of the foregoing passage (as printed in Dutch) 
has recently been copied and learnedly commented upon by 
Prof. Beijerinck (1913), who himself repeated the experiments. 
He infers that the “animalcules”? which Leeuwenhoek dis- 
covered were undoubtedly bacteria—not protozoa—and that 
among them were probably (as he found in his own experiments) 
Bacillus coli, Azotobacter, and Amylobacter saccharobutyricum. 
It was to this last species, he thinks, that the “ bigger sort ”’ 
which were found in the sealed tube probably belonged. 
Beijerinck also points out that these are the earliest known 
observations on any anaerobic bacteria: but although 

' So in the printed version. The MS. has “ for reasons already men- 
tioned ”’ (voor de verhaelde oorsaeken). 

> dierkens MS. schepsels printed version. 
* goet is in printed version, but not in MS. 
* bekennen MS. beschowwen printed version. 


Leeuwenhoek discovered that organisms could live and 
multiply under the hemi-anaerobic conditions present in his 
closed tube, he was unable at that time, of course, to realize 
the full importance of his discovery. I have also confirmed 
the foregoing observations, though I made no attempt to 
determine exactly what species of bacteria were present in 
the tubes—being satisfied with Prof. Beijerinck’s authoritative 
opinion. Iam also satisfied that no protozoa can usually be 
obtained in experiments such as the above if the procedure 
described be adhered to. 

It seems remarkable that Leeuwenhoek—always a vigorous 
opponent of the doctrine of spontaneous generation—appears 
to have made no further study of the very interesting pheno- 
mena which the foregoing experiments record. He must 
have been puzzled, at first, to account for the appearance of 
bacteria in his sealed tube: but I think his own words supply 
the explanation which occurred to him, and which apparently 
satisfied him at that time. In previous letters’ he makes the 
suggestion that ‘“‘ animalcules” or their “ seeds ”’ are present, 
or can exist, in rain—being drawn up into the clouds with 
the water in which they live or are formed, and subsequently 
scattered when the rain falls. Consequently, he probably 
imagined that the rain-water introduced into the sealed tube 
already contained ‘“ animalcules” —or “seeds”? capable of 
germinating into “animalcules”»—-which found sufficient 
‘air’ in the tube to enable them to live and breathe and 
multiply for at least some days. Nearly a hundred years 
subsequently elapsed before any further light was shed on this 
subject by the ingenious experiments of Spallanzani, though 
it was not until much later that the problem was solved— 
more or less completely—by Pasteur and Tyndall. Redi’s 
famous observations by no means solved the problem of 
spontaneous generation—as is often lightly stated: and this 
point is clearly brought out by Leeuwenhoek’s experiment, as 
he himself apparently realized; though he made no attempt— 
or, at least, recorded none—to push his inquiries any further. 

A few months after he had written the foregoing letter to 
Dr Gale, Leeuwenhoek wrote again to Dr Hooke: and in 

" Cf. Letter 18 (p. 163) and Letter 31 (p. 194). 



the course of his letter he gave some further details concerning 
the animalcules in pepper-water. His words are as follows: * 

Some days ago I once more poured water upon some 
pounded pepper; and a few days later, I saw, among 
others, two kinds of animalcules’ in it; and moreover, 
there seemed to be big and little ones of either sort,’ so 
that methought the big ones were full-grown, and the 
little ones their young; and at the same time I imagined 
that in the biggest sort of these animalcules I could see 
the young, or maybe their eggs, inside their bodies. And 
I imagined, besides, whenever I saw two little animals 
entangled together, either swimming or lying still, that 
they were a-copulating. 

* Whereas I suffer many contradictions, and oft-times 
hear it said that I do but tell fairy-tales about the little 
animals, and that there are people in France who do not 
scruple to say that those are not living creatures which I 
exhibit, and that if such water be boiled, the particles 
which one imagines to be animals still continue to move ; 
yet notwithstanding, I have demonstrated the contrary 

" From Letter 33. 12 November 1680. To R. Hooke. MS.Roy.Soc. 
Printed in Brieven, Vol. I (Dutch), and Opera Omnia, Vol. II (Latin). An 
incomplete English translation was published in Phil. Collect. of R. Hooke 
(1681), No. 3, pp. 51-58. The whole letter was first published in Dutch in 
1684 (Ondervindingen en Beschouwingen, etc. pp. 1-32): while the full Latin 
version appeared in 1695 (Arc. Nat. Det.)—It should be noted that in the 
earlier part of this letter—not here translated—L. casually mentions that 
he “ saw some little animalecules swimming” (p. 8, Dutch printed version) 
among various © globules’? which he found in rain-water that he had put in 
a special piece of apparatus. They were probably protozoa or bacteria; but 
as no further mention is made of them, they are not identifiable. 

* Evidently ciliates. 

° dat yder soorte groter en kleynder haar vertoonde printed version (1684) 
dat ijder in sijn soort bestonden uijt groote en kleijne dierkens MS. (1680). 

‘ Probably a misinterpretation of the inclusions in food-vacuoles. 

° The lines following, as far as the calculations on p. 203, have been 
translated by Hoole (1798) in his Introduction, pp.iv-vi. His rendering is 
faithful in substance, though not always in diction. In translating L. he 
allowed himself more latitude than I have done. 

LETTER 33. 12 NOVEMBER 1680 201 

to divers distinguished Gentlemen, and I make bold to say, 
that people who say such things have not yet advanced so 
far as to be able to carry out good observations. 

For my own part, I can say with truth, that the smallest 
sort of which I shall here speak, I see alive and exhibit as 
plainly to my eye as one sees, with the naked eye, little 
flies or gnats sporting in the air, though they may be 
more than a hundred million times less than a coarse 
grain of sand ; for not only do I observe their progression, 
both when they hurry, and when they slow down, but 
I see them turn about, and stand still, and in the end 
even die; and those that are of a bigger sort,’ I can also 
see running along as plain as you see mice before 
your naked eye; nay, in some I can even see the inward 
parts of their mouth, as they stick them in and out, and 
make play with them; indeed, in one sort I see the very 
hairs on their mouth, though they themselves are several 
thousand times less than a sand-grain. 

As they’ll say ’tis not credible that so great a many of 
these little animalcules can be comprehended in the 
compass of a sand-grain, as I have said, and that I can 
make no calculation of this matter,” I have figured out 
their proportions thus, in order to exhibit them yet more 
clearly to the eye: Let me suppose, for example, that 
I see a sand-grain but as big as the spherical body ABGC 
[Text-fig. 3, p. 202] and that I see, besides, a little animal 
as big as D, swimming, or running on the sand-grain; and 
measuring it by my eye, I judge the axis of ° the little 
animal D to be the twelfth part of the axis of the 
supposed sand-grain, AG ; consequently, according to the 

" From the descriptive details which follow, L. evidently refers here to 


* The beginning of this sentence—up to the point here marked—is worded 

differently in the MS. and in the printed version. The meaning is, however, 
identical in the two. 

* van (of) is here omitted from the printed version—by a misprint—but 

is present in the MS. 


ordinary rules, the volume of the sphere ABGC is 1728 
times greater than the volume of D. Now suppose I see, 
among the rest, a second sort of little animals, which 


(Text-Fie. 3.] 

I likewise measure by my eye (through a good glass, giving 
a sharp image); and I judge its axis to be the fifth part, 
though I shall here allow it to be but the fourth part (as 
Fig. E), of the axis of the first animalcule D; and so, 


consequently, the volume of Fig. D is 64 times greater 
than the volume of Fig. E. This last number, multiplied 
by the first number [1728], comes then to 110592, the 
number of the little animals like Fig. E which are as big 
(supposing their bodies to be round) as the sphere ABGC. 
But now I perceive a third sort of little animalcule, like 
the point F, whereof I judge the axis to be only a tenth 
part of that of the supposed animalcule E; wherefore 
1000 animalcules such as F are as big as one animalcule 
like E. This number, multiplied’ by the one foregoing 
[110592], then makes more than 110 million little animals 
[like F] as big as a sand-grain. 

12 10 a 1728 

12 10 + 64 
144 100 16 6912 

12 10 4 10368 

288 1000 64 110592 
144 1000 
1728 110592000 

Otherwise I reckon in this fashion’: Suppose the axis 
of Fig. Fis 1, and that of Fig. EK is 10; then, since the 
axis of Fig. D is 4 times as great as that of Fig. EH, the 
axis of D is 40. But the axis of the big sphere ABGC is 
12 times that of Fig. D; therefore the axis AG is equal 
to 480. This number multiplied by itself, and the pro- 
duct again multiplied by the same number, in order to 
get the volume of ABGC, gives us the result, as before, 
that more than 110 million living animalcules are as big 
as a grain of sand: 

1“ vermenigvuldig,’ in printed version, is a misprint. The MS. has, 
correctly, vermenigvuldigt. ; 

2 So in printed version. The MS. has merely Of anders (Or otherwise). 


axis of Fig. F = 1 
axis of Fig. H = 10 
axis of Fig. D = 40 
axis AG = 480 





However, when I took somewhat coarser sand, as I did 
when I drew up my estimate, I had to say that 20 axes 
of the foresaid | biggest] animalcules did but make up one 
axis of a sand-grain; and again, 5 axes of the lesser 
animalcule equalled the axis of the first; and further, 
10 axes of the smallest creature equalled one axis of the 
second. In fine, then, according to this calculation, a 
thousand million living animalcules are as big as a coarse 
sand-grain (taken from fine scouring sand). 

1 = axis F 
10 = axis E 
50 = axis D 

1000 = axis AG 



LETTER 71. 7 MARCH 1692 205 

In Leeuwenhoek’s next communications we find no further 
mention of either protozoa or bacteria until we come to his 
Letter 71, which, while recording various other observations, 
contains the following words: ' 

I have by me the following notes, which I feel 
constrained to add. 

For several days past I have kept in a clean glass, in 
my closet, some rain-water, gotten from a rain-cistern ; 
in which water there was a little red worm,’ which I 
divers times observed, by reason of its curious structure. 

In this water, after a day or two, a multitude of little 
living creatures did propagate themselves, they being of 
two sorts which you commonly find in fresh or sweet 
waters. The bigger sort I judged to be so small, that 
thirty thousand of them together would scarce make up a 
body as big as a coarse grain of sand. 

On several different days I did look upon these little 
animals,* and for so long, that not alone my eyes, but my 
very hands, got a-weary ; and this was simply because I 
did perceive such a plenty of these little animals, which 
were coupled together, and so long remained in this pos- 
ture: and I observed how the bigger sort dragged the 
little ones along, or swam forward with them, with the 
help of very plentevous feet, wherewith these animals are 
furnished withal ; so that 1 was thus able on this occa- 
sion to observe the copulation of these little animals 
clearer than ever before. Nay, I saw them as plain as 
you can see flying creatures* a-copulating before your 
naked eye. 

* Letter 71. 7 March 1692. To the Royal Society. MS.Roy.Soc. 
Printed in Brieven, Derde Vervolg, p. 396 (the passage here translated 
beginning on p. 423): Opera Omnia, Vol. II, p. 239 (1st pagination). A 
partial English translation was also published in Phil. Trans. (1694), 
Vol. XVIII, No. 218, pp. 194-199; but the passage here given in full is 
there so abridged that it occupies only 84 lines (on p. 198). 

> Rvidently a “ blood-worm’”’ (larva of Chironomus). 

* The animals referred to are evidently ciliates. 

* i.e. insects—not birds. 



These observations caused me to view more nicely the 
lesser animalcules that were also swimming about in the 
water, and whereof the number was a good twenty times 
as many as that of the little animals aforesaid. Some of 
these animalcules were also coupled; and I saw that 
these likewise not only stayed long a-copulating, but also 
that one of the pair, whether it swam through the water 
or ran upon the glass, dragged the other one forward, or 
trailed it after itself. 

The foregoing passage is of great interest, since it is 
evidently a record of observations made upon the conjugation 
or fission of ciliates. In my opinion the evidence is in favour 
of the view that Leeuwenhoek, on this occasion, witnessed 
both these phenomena; though it is regrettable that he 
gave so brief an account of what he saw. I cannot help 
thinking that what he interpreted as “one animalcule 
dragging another one along’ was a conjugating pair; whereas 
‘one animalcule trailing another behind it”’ was really an 
organism dividing transversely into two. Later,’ as we shall 
soon see, he described the conjugation of ciliates in unmistak- 
able terms.” 

In a letter written some 3 years afterwards, Leeuwenhoek 
mentions the discovery of “animalcules”’ in a new situation. 
After describing his observations on the oyster, and its 
generation, he remarks * : 

I also paid attention to the ordinary water that is in 
the shells of oysters; and I discovered therein a great lot 
of little animalcules, which, in bigness and figure, were 
like the little animalcules that you generally find in 
canal-water, rainwater cisterns, and common ditch-water. 
These animalcules were, in my judgement, above five 
hundred times smaller than a young oyster. 

' Cf. also the earlier observations in Letter 33, p. 200 supra. 
> Letter 96, p. 213 infra. 
* Letter 92. 15 August 1695. To Frederik Adriaan, Baron van Rhede. 

Published in Brieven, Vijfde Vervolg, p.114: Opera Omnia, Vol. II, p. 511. 
No MS., and not in Phil. Trans. 

LETTERS 92 AND 96. 1695 207 

No doubt these animalcules were protozoa: and it should 
be mentioned that Leeuwenhoek had recorded a similar 
observation at an even earlier date. Writing to the Royal 
Society about fifteen years before, he mentioned’ that he had 
found “ divers kinds of little living animalcules”’ in the juice 
of mussels and oysters: but he gave no further account of 
them, and it is impossible to ascertain what sort of organisms 
these were. It should also be noted here, however, that in a 
much later letter* he expressed the opinion that some of the 
‘“animalcules”’ which he thought he saw formerly in the juice 
of oysters were probably not really organisms at all, but 
“particles”? set in motion by the cilia on the tissues of the 

Leeuwenhoek’s last recorded observations on the “ animal- 
cules” in infusions are contained in a letter written several 
years later, and sent not to the Royal Society but to the 
Elector Palatine. This very interesting letter runs as follows’: 

In my letter of 18 September’ [1695] I ventured most 

respectfully to describe how I opened a Freshwater 
Mussel° and took out of it the unborn young mussels,’ 

* Letter 30. 5 April 1680. To Robert Hooke. MS.Roy.Soc. Published 
in Brieven, Vol. I, p.33 (1st pagination): Opera Omnia, Vol. I, p. 25 (2nd 
pagination): English abstract in Phil. Trans. (1693), Vol. XVII, No. 196, 
p. 593. 

* Letter dated 10 June 1712. To the Royal Society. MS.Roy.Soc. 
English version printed in Phil. Trans. (1712), Vol. XXVII, No. 336, p. 529. 
Not published elsewhere, and not numbered by L. himself. 

* It seems to me probable that L. was here referring to the observations 
contained in Letter 30, and not to those in Letter 92, which appears to record 
a genuine observation of protozoa. 

* Letter 96. 9 November 1695. To the Elector Palatine. Published 
in Brieven, Vijfde Vervolg, p. 156: Opera Omnia, Vol. II (Contin. Arc. Nat.), 
p.30 (2nd pagination). Not translated by Hoole. No MS., and not in 
Phil. Trans. I translate the whole letter, with the exception of a few 
immaterial words at the beginning and end. 

° Letter 95, printed immediately before the present letter in L.’s published 

* Veen-Mossel (literally ‘‘ fen-mussel’’) — Anodonta: not easily recog- 
nizable in the Latin version, where it is called “ concham ex genere earum 
quae ex fossis capiuntur.”’ Veen means not only a fen, marsh, or bog, but 
also the peat which can be dug out of such places: and consequently Hoole 
(Vol. I, p. 85 sq.) translates veen-mossel as ‘ peat-muscle.’”’ But Anodon was 
never known by this name in England—so far as I am aware. 

" i.e., the “ Glochidia ’”’ larvae—described and figured in Letter 95. 




which had developed so far that I judged them to be com- 
pletely formed, because their shells seemed to be perfect. 

I took several thousand of these unborn mussels, and 
put them in a glazed white earthenware basin, and forth- 
with poured canal-water upon them, in order to see 
whether any of these unborn mussels would remain alive 
and grow bigger. 

Having put these little unborn mussels in the water, 
I viewed them on several successive days, yet I could 
make out no change in their size. But since, owing to 
the rain which had fallen plentifully, our canals were 
filled at that time with no other water than what runs 
off the land, and which must then flow through our Town, 
I saw, beyond my expectations, a great many very little 
living animalcules, of divers sorts and sizes, in this water, 
a-swimming among the unborn mussels. Amongst others 
I saw some little worms,’ having a figure very much like 
those worms that children void in their stools,” but whose 
thickness I judged to be a quarter of that of a hair off 
one’s head. 

Furthermore, I saw some animalcules stuck fast to 
one another by their long tails*; and these animalcules, 
as well as sundry other sorts, I had never seen before, and 
their motion was uncommon pleasant to behold. 

Further, I saw that these animalcules did increase in 
numbers from day to day. 

At first, after four or five days, I replenished the water, 
wherein these unborn mussels Jay, in such a fashion 
that I poured off all but about a spoonful* of it, and then 
presently added more canal-water again thereto. 


Probably free-living nematodes. 

* Probably meaning the nematode Oxyuris (=Enterobius) vermicularis. 


Evidently a colonial Vorticellid (Carchesiwm ?). The “ animaleule with 

a tail” is L.’s name for Vorticella, already described in Letter 18 (p. 118). 
Further observations on the colonial forms are recorded later in the present 
letter. (See also p. 277 sq., infra.) 

* op een lepel vol water na Dutch version omnem fere aquam Latin 

LETTER 96. 9 NOVEMBER 1695 209 

In these my inquiries, I imagined that the unborn 
mussels got eaten up by the little animalcules aforesaid ; 
because it oft-times happened that I saw a multitude of 
little animalcules that had got between the shells of the 
young mussels, so that I judged, indeed, that I could even 
see as many as fifty animalcules inside a single young 
mussel. And during my observations, I observed that the 
fishy matter in the unborn mussels got less from day to 
day; nay, to such an extent even, that after the lapse of 
twelve days, little or no fishy matter was to be discerned 
between their little shells, which had become all trans- 
parent. After this time, too, I could not perceive that 
the animalcules were increasing in such great plenty. 

My notion that the little animals were partly the cause 
of the unborn mussels being eaten up (though ten 
thousand of the little animals aforesaid would, for the 
most part of them, scarce equal in bigness one of the little 
mussels), was confirmed when I came to inspect the little 
mussels (at the time when I had placed them in water in a 
white Delft porcelain basin) after inclosing them in various 
little glasses*; whereupon I perceived that each little 
mussel inclosed in the little glass, though also lying in 
water, still had its fishy substance between its shells, 
notwithstanding that many of them had their shells wide 
apart, or agape. 

I have sometimes been puzzled when beholding the 
multitude of little unborn mussels which lay inclosed in a 
big mussel ; for I was not able to conceive why our canals, 
and fens, are not overflowing with mussels, seeing that the 
water does not run so strong that it could carry the little 
mussels along with it, while they are still very small ; 
and in the second place, seeing that they are not gathered 
to serve as food: so that one mussel ought to beget 
thousands. But now, after discovering how the little 

" As mentioned below, these “little glasses” (glaasjens) were capillary 
glass tubes, such as L. commonly employed in his experiments. 



animals aforesaid devoured them, methought this a 
sufficient reason why freshwater mussels are not found in 
ereater plenty.’ 

After this, I let the water stand for twelve more days, 
without replenishing it, in order to see whether, if I did 
so, the animalcules would multiply in greater numbers. 
But I perceived that the animalcules decreased from day 
to day; so that by the 8th of October they were indeed 
grown so few, that where I had before discovered a good 
hundred of them, I now could scarce see one; and those 
of the biggest sort, which still remained over, moved 
forward very slow, and were very thin in the body; and 
all the little shells of the unborn mussels had so far 
increased in transparency, that I could make out some 
hundreds of very little parts, whereof they were composed. 
And so, from all these observations, I concluded that 
all the various animalcules had now died for lack of food. 

In order to satisfy myself further concerning the 
plentevous multiplication of the little animalcules, and 
in so very short a time, I took a parcel of canal-water, 
somewhat more than a common wine-glass full, and put 
in it an ordinary mussel, that I had taken out of its shell’ ; 
and I put this mussel in the water to see, if ’twere 
possible, whether the animalcules would multiply beyond 
what they commonly do, owing to the food that they 
would be able to get from the mussel. 

After the mussel had lain for four-and-twenty hours in 
the water, I took a little of the uppermost part of the 
water, and examined it through the microscope; and I 

' From these observations one can hardly doubt that L. had got 
something more than an inkling of the part played by putrefactive micro- 
organisms in the general oeconomy of nature. To appreciate the novelty 
of this notion—nowadays commonplace— one must remember that it belongs, 
historically, to the nineteenth century. 

? In such an infusion of freshwater mussel many different Protozoa are 
commonly found, including ciliates (e.g., Paramecium) and flagellates (e.g., 
Trepomonas). For this reason it is impossible to determine what particular 
forms L. was likely to have seen. 


saw, to my wonder, a vast number of animalcules. And 
after the water, with the mussel in it, had stood for twice 
twenty-four hours, I observed that the number of animal- 
cules was greatly increased. I took a little of this water, 
and put it in a glass tube, whose diameter was about 
a fifteenth of an inch, and which was filled for about an 
inch of its length with the water. In this water I saw a 
few little animalcules swimming, whereof several thousand 
together would scarce equal a sand-grain in bigness. 
These animalcules had a pretty structure, for the round 
circumference of their bodies seemed to be made up of ten 
or twelve brighter round pellets, while in the middle of 
them there seemed to be a little dark spot, somewhat bigger 
than the pellets. These animalcules generally rotated 
themselves in their progression (which took place 

When these animalcules had been a little while in the 
foresaid glass tube, I saw a slender little structure like 
unto a little branching vein, with seven or eight lesser 
branches, each several little branch being full a hundred 
times thinner than a hair off one’s head; and at the same 
time I saw that at the utmost extremity of every little 
branch, one of the forementioned little animals was firmly 
fixt, though at first I could discover no motion in ’em. 
Yet after the lapse of about a minute, I perceived that 
some animalcules began to move themselves to and fro, 
whereby each of the thin little branches became bent 
into divers coils. The longer this motion continued, the 
stronger it became, till at last the little creature, by its 
efforts, got loose from the little branch, and swam off; 
and the same thing came to pass with all the others too, 
so that the little branching structure was forsaken by all 
the animalcules that were discernible.” 

i T 

’ Probably ciliates—the bright bodies being food-inclusions, and the dark 
central spot the meganucleus. 

* This graphic narrative gives an unmistakable description of Carchesvwm. 





From this spectacle, I imagined that the little animals 
of this kind must have laid their little eggs, or young 
animalcules, upon the ends of every little branch, and 
that they had there waxed in bigness, and grown up. 

Furthermore, this little branching vein was for the 
most part clothed with a clearer matter, which I judged 
was made up of round pellets. Seeing this, it came into 
my head that all the round particles which I could see 
might perhaps be really eggs, or young animalcules, and 
that from these particles, moreover, similar animalcules 
might presently come forth. After the lapse of another 
twenty-four hours, I looked upon the little branch again ; 
and I then saw that some animalcules, which had reached 
their full growth, were fixed anew upon it; and that 
many of these animalcules were swimming around the 
little branch, while the roundish particles, that I’d seen 
on the branch the day before, were much diminished in 
number.’ ; 

At a distance of about half an inch from the little 
vein-branch aforesaid, there lay in the water a little fibre, 
whereon were also fixed some little animals; and these too 
were come forth (so I imagined) from the round corpuscles 
which were likewise fixed to the fibre. These animalcules 
were increased to such great numbers in the space of 
twice twenty-four hours, that I now saw quite fifty of 
them where I had before seen but one. 

Now, as we have made sure that, in twice twenty- 
four hour’s time, animalcules appear, which have reached 
their full growth; and as we imagine that they have 
come forth from little round particles: therefore, we need 
not wonder at the multifarious little animalcules which 
we perceive to be bred in water in only a few days’ time 
(provided only that food be not lacking for them). And 
who knows but what one sort of these very little water- 

The observations here recorded were, no doubt, perfectly accurate : 

but the interpretation which L. put upon them is, of course, incorrect. 


creatures may not gobble up another sort, using it as 
food,’ just as we see that big fish do? For, an ’twere 
otherwise, the water would get stuffed full with little 

One day afterwards I looked at the animalcules again, 
and saw, to my wonder, that many of ’em were coupled; 
nay, some of ’em even coupled before my eye; and at the 
beginning of their copulation they had a wobbling motion, 
but after coupling swam forward together, and did stay 
still too, fixt to the glass.’ 

At this time I saw also that the bodies of each animal- 
cule of the pair were of a roundish figure ; for no matter 
how they turned about in swimming forward, they always 
kept one and the same shape, looking like a little round 
cluster of grapes, the cluster being stuck together very 
tight; and as the animalcules swam forward, you saw each 
of the supposed grapes in motion. 

"Twas eventide when I carried out the observations 
last mentioned; and next day, in the morning, I found 
that many of the animalcules were dead, and by evening 
they were so diminished, that I could find but four of 
them that were still alive: wherefore I concluded, that the 
little creatures were died off for want of food. After 
another night had passed, I saw but one animalcule living ; 
and the bodies of all the dead animalcules in the water 
were so gone to pieces, that I saw nought but little round 
particles (as they seemed to my eye), which made the 
water, wherein these little animals had been swimming, 
all troubled. 

' As the “ bigger sort’ were, in part, ciliates, while the “smallest sort ”’ 
were bacteria, L.'s conjecture here was perfectly sound. 

* This passage proves conclusively that L. observed the conjugation of 
ciliates. In his earlier observations he had only seen the organisms joined 
together; and consequently he may have seen ciliates really undergoing 
fission—not conjugating. But here he says he actually saw them come 
together, so that there can be no doubt as to the correctness of his 


Two days after the foregoing discoveries, I again beheld 
the small parcel of water aforesaid in the glass tube; and 
as I did so, I saw a huge number of extreme small fishes, 
or animalcules, which I may call little eels,’ because in 
swimming forwards they lashed their bodies like eels 
do, and so quick that ’twas marvellous. These little fish 
did mostly stay close beside one another, and round the 
circumference of the tube, and in vast numbers; and in 
my judgement their length was equal to the diameter 
of one of those blood-globules which make the blood red. 
And they remained alive some seven days, after which 
time I could make out only one every now and then. 

Among these little animals, or little fishes, I did also 
see a-Swimming a few smaller animalcules, whereof I 
deemed that eight of ’em together were no bigger than 
the said blood-corpuscle*: and now I could no longer 
discern that little structure that I heretofore likened to a 
little branching vein, how oft soever I looked for it. 
These last-mentioned animalcules were so prodigiously 
increased in two or three days, that ‘tis incredible ; though 
by now half the water was evaporated away. 

All the water that I have so far spoken of, which I had 
put in the glass tube, and wherein the foresaid multi- 
plicity of little animalcules were bred, I deemed (to the 
best of my knowledge) to be no more in bulk than the 
eighth part of a green pea; but not being content with 
this my estimate, I went and weighed a like quantity of 
water, and I found its weight two grains. I did also 
weigh some peas, and found that a common pea weigheth 
eight grains. 

Through the microscope with which I had carried out 
the first observations, I imagined I still saw,* in water 

* Probably Spirilla—certainly bacteria of some sort. 

* i.e., their diameter was about half that of a red blood-corpuscle. 
Undoubtedly bacteria. 

° L., it will be recalled, commonly used a different microscope for each 
separate observation—the object being more or less permanently fixed and 
focussed before the lens. 


taken from the surface of that wherein the mussel lay, a 
vast company of living animalcules: but to make sure of 
this, | made use of a glass of higher magnification, and 
a different instrument: and I then saw so great a many 
of such extreme small animalcules,’ that there’s no man 
living could possibly conceive of them; nay, they were so 
little, that several millions of them together would not be 
as big as a coarse grain of sand. Nevertheless, all these 
animalcules, when I put them in a glass tube, remained 
alive but a little while. 

Moreover, I found that the animalcules in the water 
that the mussel was in, had increased so much in seven 
or eight days, that I might well say their number was (to 
the best of my judgement) quite ten times a hundred 
thousand more than those in the water before I put the 
mussel in it. 

Regarding this increase of animalcules in water, and in 
so very short a time, I have oft-times been amazed: and 
especially, because I chanced to see divers sorts of 
animalcules, which increased in numbers, without being 
able to discern any of them that were smaller; all of 
them being of an equal bigness.” 

But after observing what I have just related (namely, 
that there are animalcules which do not take to swimming 
about till they have reached their full growth, and 
which soon after are ready to copulate; and therewithal 
that a full-grown animalcule is produced in one night), I 
was now, to my great satisfaction, delivered from all 
those difficulties, that I had for years laboured under, 
concerning the generation of these little creatures. 

When I first discovered, in the year 1675, a great 
plenty of divers very little animalcules in water, and 
made these observations known by letter to the Royal 

’ Bacteria. 

* He means that he could detect no young ones of any species. 


Society in London, neither in England’ nor in France 
could they accept of my discoveries: nor do they even yet 
in Germany, as I’m informed. 

This remarkable document ends at this point with a couple 
of extracts from Leeuwenhoek’s letters of 23 March 1677 (to 
Oldenburg) and 5 October 1677 (to Lord Brouncker), which 
were sent to the Elector Palatine “to give him greater 
satisfaction concerning the vast numbers of little animalcules 
that are found in water”: but as these letters have already 
been given fully on earlier pages,’ it is unnecessary to repeat 
them here. 

With these observations we come to the end of Leeuwen- 
hoek’s researches on the free-living Protozoa and Bacteria, in 
so far as they were made in the XVII Century. Later he 
made many notable additional observations, but these will be 
chronicled in a later chapter: and we must now retrace our 
steps in order to record his equally wonderful discoveries 
concerning the parasitic Protista. 

* This can hardly be regarded as a fair description of the reception 
accorded to L.’s earliest observations by the Fellows of the Royal Society. 

* Vide pp. 168 and 173 supra. The second letter was originally addressed 
to Oldenburg, but redirected to Brouncker when L. heard of his death. 




(Lerters 7, 33, 34, 38, 39, 75, 110, etc.) 

E have already seen (in Chapter 1) how Leeuwenhoek 
NV discovered the free-living Protozoa and Bacteria. 
We inust now chronicle his discoveries in the world 

of similar “ parasitic’ organisms.’ 
It will be remembered that Leeuwenhoek first saw protozoa 
in water in the summer of 1674.* He probably first saw a 
parasitic protozoon—though he had no idea what it was—in 
the autumn of the same year. Whilst examining the bile of 
various animals, he hit upon some curious structures which he 
described, in the course of a rather rambling letter, in the 

following terms: * 

The bile of a cow was examined* by me on the Ist 
instant,’ and therein I beheld some few globules” that 
floated in the liquid ; but I didn’t see them unless I set the 
bile in a continual motion before my sight, for ’twould else 
have been impossible for me to perceive the globules in it, 

* To call all such micro-organisms studied by L. by the opprobrious 
name of © parasite” is hardly justifiable, for most of the forms which he 
described cannot be regarded as harmful. They are “ parasitic” in a 
colloquial and unscientific sense only. 

” See p. 109. 

> From Letter 7. 19 October 1674. To Oldenburg. MS.Roy.Soc. 
This letter was wholly unpublished until recently, when I first published 
(Dobell, 1922) the passages given here in revised translation. 

* i.e., with the microscope. 

° 4.e., 1 October 1674. 

° clootgens MS. 




because they were so few in the bile that I was examining. 
But afterwards, examining the bile of another cow, I 
found that the globules were of a heavier matter than the 
liquid that they floated in; wherefore I drew off the bile 
from the bottom of the gall-bladder, and then found that 
there were' many hundred times more globules in this 
bile than in that which I had taken from the upper part 
of the gall-bladder; and there were, besides, some 
corpuscles * which, to my eye, looked as big as ants’ eggs.” 
These had the figure of an egg,* only with this difference, 
that whereas an egg is more sharply pointed at one end 
than at the other, yet these corpuscles were equally 
pointed at both ends: and moreover these corpuscles 
were composed of globules joined together, and had a 
yellow colour, except several which were somewhat 
whitish ; but notwithstanding, they were so transparent 
that you could see the body of one through that of 
another. And this transparency making me wonder 
whether they might not, in fact, be little vesicles filled 
inside with liquid, I fished some of these corpuscles out of 
the bile with a fine hair; and looking at ’em on the hair, 
I perceived two which seemed to be pushed in, just as 
though you had blown up a bladder and then stuck your 
thumb in it, so as to make a dent in it; whereupon I was 
the more firmly persuaded that these corpuscles were filled 
with some sort of humor. Afterwards, on examining 
more biles from oxen, I found them the same as before; 
only with this difference, that one bile might be furnisht 
with more of the oval corpuscles than another. 

was MS. 

* deeltgens MS. 


L. means that the objects looked, under his microscope, about as big 

as ‘ants’ eggs” look to the naked eye. At a later date he published a 
remarkable account of ants, from which it is clear that he was well aware 


the ant’s “egg” is not really an egg, but a pupa. See Letter 58, 

9 Sept. 1687. 


: ) 
2.€., a hens egg. 

LETTER 7. 19 ocToBER 1674 219 

In the bile of two calves I find, furthermore, some very 
little globules floating, and very many irregular particles 
of divers forms; among others, some like little floating 
clouds, all consisting of very little globules joined together. 
On seeing these irregular congealed particles, I judged 
them to be joined or stuck together through no other 
cause than because the bile had got cold, and was without 
motion. In the bile of a third calf there wére a few oval 

Moreover, in the bile of sucking lambs I find there are 
very little globules, and some, though very few, bright 
particles, which are a bit bigger; besides irregular particles, 
of divers figures, and also composed of globules clumped 

The bile of a yearling sheep I find to be like that of 
sucking lambs, only with this difference, that in this bile 
there are also oval corpuscles of the bigness and figure of 
those that I remarked in ox-bile. 

I have examined the bile of two young rabbits: that of 
the first was inclined to a purple colour, and in it I beheld 
very many globules, and irregular particles made up of 
globules clumped together, which were of various red 
colours:* and this diversity of colour I imagined to be 
due to no other cause than that some of these compound 
particles, being made up of more globules, were denser 
than the rest. In the other bile the irregular particles 
were fewer, but there were more globules and the colour 
was a light reddish. 

Further, I examined the bile from three old rabbits. 
The first had a very few small globules, but very many 
oval corpuscles of a figure like those that, as I have said, 
I saw in the bile of a cow. In the bile of the two other 
rabbits there was nought but globules, and irregular 

* Evidently red blood-corpuscles. LL. had described these—from his 
own blood—in another letter written earlier in the same year (Letter 3, 
7 April 1674). An English abstract of this appeared in Phil. Trans. (1674), 
Nol. EX. No. 102. pn. 23: 



particles made up of globules joined together; though 
the thin matter’ of one was much thicker and stickier 
than that of the other, and there were some little clouds 
floating through it. 

I have furthermore examined the biles of fowls, 
turkeys, ete., and in them I also found very little 
globules floating, and irregular particles composed of 
globules stuck together. 

I think there can be no doubt that the “ oval corpuscles ’”— 
called eyronde deeltgens in the original—which Leeuwenhoek 
discovered in the gall-bladder of one of his “ three old rabbits,” 
were the oocysts of the coccidian Himeria stiedae; while the 
comparable structures which he found in the bile of sheep and 
oxen were, equally certainly, the eges of trematodes.” But as 
I have already discussed this subject in some detail elsewhere,’ 
I shall say no more about it here. If my interpretations be 
correct, then the foregoing extract records the first observations 
ever made upon the Sporozoa or upon any parasitic protozoon. 

It is true that Leeuwenhoek himself did not realize that he 
had discovered a stage in the life-history of a brand-new kind 
of parasite: but the same can be said also of others who are 
now generally credited with the discovery of the Coccidia.'* 
The fact remains, none the less, that he saw and described— 
though his description was not published for nearly 250 years— 
a coccidial parasite long before all other men. 

* i.e., the liquid part of the bile. 

* Fasciola hepatica—the worm itself—was well known to L.; for the 
Dutch anatomist Bidloo (1649-1713) dedicated a little memoir to him, in 
1698, in which it was described and figured. At a later date, L. himself 
wrote a letter to the Royal Society on the ‘ Worms observ’d in ae 
Livers ’’—of which an English abstract was published i in Phil. Trans. (1704), 
Vol. XXIV, p. 1522. The original letter is extant, and is dated 3 Nov. 
1703. It was not included in the Dutch or Latin collected works. 

* See Dobell (1922). 

“ The lesions of hepatic coccidiosis in the rabbit appear to have been 
first depicted by [Sir] Robert Carswell (1793-1857 ; Professor of Pathological 
Anatomy at University College, London) in the year 1838. He regarded 

them as “the seat of tuberculous matter.” The oocysts of E. stiedae were 
first figured and described in print by Dr Thomas Gordon Hake (1809- 


Leeuwenhoek’s next observations on ‘ animalcules”’ 
inhabiting the bodies of other animals were written down 
in 1680 and printed some few years later. ‘They occur in the 
course of his description of the spermatozoa of insects—various 
species of which he dissected in his attempts to study their 
“seminal animalcules”. After recording some findings in 
flies, he casually adds the following: ' 

I have also seen, in the summer,’ in a big horse-fly 
(which was a female, out of which I pulled many eggs), a 
lot of small animalcules ; though these were not a sixth 
of the length of the animalcules aforesaid,* but a good 10 
times thicker.* They lay mingled with the thin matter ” 
that was in the fly’s guts, and moved forwards very 

From the size and proportions of the “ animalcules”’ here 
mentioned, and from their situation, it can hardly be doubted 
that Leeuwenhoek actually saw on this occasion a protozoon 
(or possibly a bacterium) in the gut of a horse-fly. The 
dimensions of the organism are against the bacterial inter- 
pretation, but agree very well indeed with the supposition that 
he saw a Orithidia (or Leptomonas).° If this was so, then we 

1895; a practising London physician, and English minor poet) in 1839. 
He interpreted the lesions as “carcinoma”, and the oocysts as “a new 
form of the pus globule.” See Dobell (1922). 

* From Letter 38. 12 November 1680. To R. Hooke. MS.Roy.Soc. 
Published in Brieven, Vol. I (Dutch), and Opera Omnia, Vol. II (Latin). 
The full letter first appeared in print (in Dutch) in 1684. An incomplete 
English translation was published earlier, however, in Hooke’s Phil. Collect. 
(No. 3, pp. 51-58; 1681). The passage here translated is on p. 23 of the 
Dutch printed version. 

* Presumably 1680. 

° L. here refers—as the context shows—to the spermatozoa of “ the 
smallest sort of our common house-fly.”’ 

* On L.’s system this means that they had rather more than thrice the 
diameter of the fly’s spermatozoa. 

° 4.e., liquid or watery material. 

° These flagellates oceur—as is now well known—in many different 
species of Tabanidae. Several species of Crithidia have been described, in 
recent times, from the intestines of HKuropean species of Tabanus.—I may 
add that, forty years ago, Biitschli (1887-89; Vol. III, p. 1101) pointed out 
that the organisms here described by L. were probably flagellates; but he 
wrongly dated the observations 1695—the date of publication of the first 
Latin translation. 


have here the first recorded observations ever made upon any 
protozoa belonging to the important flagellate family of the 
Trypanosomatidae. But this interpretation, though very 
plausible, is not absolutely certain ; for the details recorded 
are obviously too scanty to warrant dogmatic deductions. 
Nevertheless, it can, I think, be concluded—with complete 
assurance—that Leeuwenhoek observed “ parasitic” protists 
of some sort in the intestine of a horse-fly as early as the 
year 1680. 

We now come to a letter of great historic interest and 
importance—a letter which has rarely been read aright, but 
one which records in no uncertain terms the discovery of the 
intestinal protozoa and bacteria of Man. This letter was 
written in 1681, and in it Leeuwenhoek discusses a variety of 
subjects—such as the structure and falling-out of the hair, 
“blackheads ”’ (comedones), clay, and gout: but the only part 
which here concerns us deals with the discovery of “living 
animalcules in the excrements.” ‘The passages in question 
run as follows:' 

I weigh about 160 pound, and have been of very nigh the 
same weight for some 30 years,” and I have ordinarily of 
a morning a well-formed stool; but now and then hitherto 
I have had a looseness, at intervals of 2, 3, or 4 weeks, 
when I went to stool some 2, 3, or 4 times a day.’ But 

* From Letter 34. 4 November 1681. To R. Hooke. MS.Roy.Soc. 
Published in fullin Brieven, Vol. I (Dutch), and Opera Omnia, Vol. I (Latin). 
The Dutch version first appeared in 1686 (Ontled. en Ontdekk.), the Latin 
[from which the date of the letter was omitted ] in 1687 (Anat. s. Int. Rerwm). 
An English abstract was published by R. Hooke in Phil. Collect. (1682), 
No. 4, p. 93: and another by Derham in the posthumous Phil. Expts. and 
Obss. of Hooke (1726), p. 61. The letter itself was presented to the Society 
at their meeting held on 2 Noy. 1681, and read in English translation at the 
following meeting on Nov. 9 [O.8.]. Cf. Birch, Vol. IV, pp. 99, 101. Part 
of this letter was also translated by Hoole in his Select Works of L.—but 
not the part with which we are now concerned. I have already translated 
and commented upon the paragraphs dealing with intestinal protozoa 
elsewhere (Dobell, 1920). 

* When he wrote this L. was 49 years old. 

* The Latin version of this passage is somewhat ambiguous, and has 
apparently led some readers to suppose that L. frequently suffered from 
diarrhoea lasting for 2-4 weeks at a stretch. It has even, indeed, given rise 
to the belief that he suffered from chronic dysentery for 30 years. His own 
words do not countenance any such conclusions. Cf. Dobell (1920). 

LETTER 34. 4 NOVEMBER 1681 293 

this summer! this befell me very often, and especially 
when I partook of hot smoked beef, that was a bit fat,” or 
ham, which food I’m very fond of; indeed, it persisted 
once for three days running, and whatever food I took, I 
kept in my body not much > above 4 hours; and I 
imagined (for divers reasons) that I could get myself well 
again by drinking uncommon hot tea, as hath happened * 
many a time before. 

My excrement being so thin,’ I was at divers times 
persuaded to examine it ;° and each time "T kept in mind 
what food I had eaten, and what drink I had drunk, and 
what I found afterwards*: but to tell all my observations 
here would make all too long a story. I will only say that 
I have generally seen, in my excrement, many irregular 
particles of sundry sizes, most of them tending to a round 
figure, which are very clear and of a yellow colour :’ these 
were the ones that make the whole material look yellow 
to our eye. And there were also, besides, suchlike 
particles that were very bright and clear, without one 
being able to discern any colour in them.” 

I have, moreover, at divers times seen globules that 
were as big as” the corpuscles in our blood, and that each 


" i.e., anno 1681. 


dat een weynig vet was. These words are in the printed version but 

not in the original MS.—A similar remark is made by L. much later in 
Send-brief XX XIX, 13 July 1717, to J. G. Kerkherdere. 


veel is here in the printed letter, but not in the MS. 

‘ is gelukt [=succeeded] MS. is geschied [ =befell] printed version. 

> 7.e., dilute or watery. 





i.e., with the microscope. 

soo nu en dan MS. soo nu als dan printed version. 

This word is not in the originals. I add it to preserve the sense. 
Probably incompletely digested remains of meat (striated muscle). 

0 fe., the faeces en masse. 
11 Pyobably fat-droplets. 

12 The Latin version mistranslates soo groot als as ° bigger than” 
(globulos globulis nostra sanguinis majores vidi). 


of them was made up of 6 separate globules :' and further, 
there lay, among all this material, globules whereof 6 of 
‘em together would make up the bigness” of a blood- 
corpuscle. These last were in such great® plenty, that 
they seemed to form a good third of the whole’ material: 
while there were besides many globules which were so 
small, that six-and-thirty of ’em would make up the bigness 
of a blood-globule.’ 

All the particles aforesaid lay in a clear transparent 
medium, wherein I have sometimes also seen animalcules ° 
a-moving very prettily; some of ‘em a bit bigger, others 
a bit less, than a blood-globule, but all of one and the 
same make. ‘Their bodies were somewhat longer than 
broad, and their belly, which was flatlike, furnisht with 
sundry little paws, wherewith they made such astir in the 
clear medium and among the globules, that you might e’en 
fancy you saw a pissabed‘ running up against a wall; and 
albeit they made a quick motion with their paws, yet for 
all that they made but slow progress. Of these animalcules 
I saw at one time only one in a particle of matter as big 
as a sand-grain; and anon, at other times, some 4, 5, or 
even 6 or 8. I have also once seen animalcules of the 
same bigness, but of a different figure. * 

* At one time L. held the curious belief that each red blood-corpuscle 
was composed of 6 aggregated smaller “globules”. This was an error 
probably due, I think, to misinterpretation of diffraction-images. 

* i.e., in volume—not in diameter. 

* groote stands here in the MS. but not in the printed letter. 

* gantsche MS. omitted from printed letter. 

° 7.e., their diameter was between + and + of that of a human red 

* The following description—as I have elsewhere tried to show (Dobell, 
1920)—is a graphic account of the flagellate Giardia (=Lamblia) 

" The woodlouse or sow-bug (Oniscus asellus). The Latin translation of 
this passage has given rise to many curious misunderstandings. Cf. Dobell 
(1920), where “ pissabeds”’ are more fully discussed. 

* As no other details are given, it is impossible to identify these 
organisms. Possibly they were Trichomonas or Chilomastiz. 


I have also seen a sort of animalcules that had the 
figure of our river-eels: these were in very great plenty, 
and so small withal, that I deemed 500 or 600° of ’em 
laid out end to end would not reach to the length of a full- 
grown eel such as there are in vinegar.” These had a 
very nimble motion, and bent their bodies serpent-wise, 
and shot through the stuff as quick as a pike does through 
the water.’ 

At another time I saw, in 4 several observations, but 
one animalcule of the sort first spoken of;* but at my 
fourth observation, observing more narrowly than before, 
I saw a great number of animalcules,’ each of which I 
judged to be more than 200 times less than a globule of 
our blood: for I imagined that I could make out that the 
length of six diameters of one animalcule couldn’t reach 
beyond the diameter of one blood-globule. But here I 
speak to those who are versed in geometry, and know full 
well that if the diameter of one body be 1 and that of 
another (of like figure) be 6; then the difference in their 
bulk is as 1 to 216. And I can’t forbear to say that I 
have divers times judged that I have seen, with great 
delight, in a particle of matter of the bigness of a coarse 
sand-grain, more than 1000 living animalcules, and these 
of 3 or 4 sorts, all alive together; nay, you might well 
have supposed that the whole material consisted of nought 
but living animalcules. Some people hearing this might 


* The Latin version wrongly says “50 or 60” (quinquaginta aut 
secaginta), which would—if correct—-put a very different complexion on 
this passage. 

> Anguillula aceti, the “ vinegar-eel’’. Cf. p. 150 swpra. 

? From the description here given, it can hardly be doubted that these 
organisms were spirochaetes. In recent years a vast literature has sprung 
up on the intestinal species in man; but it must suffice to note here that 
more than one species occurs in human faeces, and that spirochaetes of 
some sort are normally present in the intestines of most human beings. 
This is the first record of their occurrence. 

* Referring to Giardia. 

> Probably bacteria, but possibly inanimate particles in Brownian 



perhaps imagine that these animalcules, because of their 
extreme littleness, might well get through into our blood ; 
but I conceive that the vessels which conduct the material 
(out of which blood, fat, etc. is made) are so small, or must 
pass through such narrow channels, that even if such a 
little animalcule were divided into more than 1000 parts, 
‘twould still be too big to get through them.’ 

I have, moreover, examined my excrement when it was 
of ordinary thickness, and also mixed with clean water, 
but could then discover no animalcules in it; but 
whenever the stuff was a bit looser than ordinary, I have 
still seen animalcules therein, contrary to my expectation. 
I have, however, also seen in it some particles of food that 
were not digested; among others, for example, after I had 
eaten asparagus I saw very prettily its little tubes (off 
which the soft parts had been all digested away). 

At divers times in the summer I have betaken myself 
into our meadows, and collected the dirt of cows and 
horses, just as they let it drop; yet I could discover no 
living animalcules therein, but most of this stuff (setting 
aside grass-particles which were undigested) was made up 
of globules, whereof 6 would be as big as a blood-globule, 
and many lesser globules of which I judged that 36 
together would be only as big as a blood-globule; all these 
lying in a clear medium. 

In the month of May,’ I rode my horse (which is a 
mare) very hard, for about 1% hour’s going;° and on 
getting back to the stable, she let go her urine; and as 
the last of this urine looked to me very thick, and was 

" L. means that the channels—in the intestinal wall—through which 
the ultimate food-particles in the gut pass into the blood-stream are too 
minute for bacteria to traverse them: and that even if a bacterium were 
but a tenth of its length, it still would be too big to do so. 

> Presumably anno 1681. 

* 14 wre gaens MS. The printed version says “an hour and a quarter ’ 
(een en een quart van een ure). Apart from this discrepancy in the time, it 
should be noted that L. does not mean that he rode his mare hard for an 
hour and a half (a pretty strenuous feat), but for a distance equal to that 



of an ashen colour, I viewed it’ through a common 
microscope, that I had by me; and I found that what 
gave it the ashen colour were globule-like particles, of 
sundry sizes, each of ’em made up of still lesser globules 
stuck together. And these last globules were as big as 
the globules of our blood, and each of these again consisted 
of six several globules. I can’t describe the first sort of 
globules better than by likening them to a round bunch 
of grapes, growing very close together, as it looks to your 
naked eye ; and although the particles were not perfectly 
round, yet I may call ’em globules, for they were wanting 
in nothing but that those which were as big as a blood- 
globule (which I have already described as compound) 
stuck out a bit on the outside, like each grape does from 
its bunch.” Of this matter I took up a little, and found 
that besides the globules aforementioned there were yet 
many others, which had a sixth of the bigness of one of 
our blood-globules, and also some whereof I judged that 
36 of ’em together would only make up the bulk of a 

which would be covered in an hour and a half by a man on foot. (Cf. note 
3 on p. 109 supra.) The Latin translator—who copies the time from 
the printed Dutch version, not the MS.—accordingly renders this phrase 
(correctly) as “ circiter horam atque horae quadrantem pedestris itineris. . .” 

' In an earlier communication (Letter 38, 12 Noy. 1680), L. mentions 
that he examined his own urine, at a time when he was sick, and found in 
it—in addition to numerous particles—several red blood-corpuscles (ef. p. 12 
of Dutch printed version). 

* This is a hard sentence to translate closely and intelligibly. I give it 
as near as I can—without improving it too much. 

* The foregoing observations—though they record the discovery of no 
new animalcules—appear to me to be of great importance; for they show 
that L. really recognized living bacteria when he saw them. He did not 
here—or elsewhere—mistake minute inanimate particles for “‘animalcules.”’ 
At first sight it may seem strange that he did not take all minute moving 
particles for living organisms—as would have been indeed excusable. 
‘“ Brownian movement’ was not “ discovered ” until a century and a half 
later: but the phenomenon itself must have been frequently witnessed by 
L. He accounted for it as a consequence of the heat imparted to his 
microscopic preparations by their proximity to his own body. (He had to 
hold his microscopes very close to his face, because of the very short focus 
of his lenses.) 




I then bethought me to examine the dirt of hens; and 
in order to get it clean, I squeezed the dirt out of a fowl’s 
body as soon as it was dead. On viewing it, I saw 
therein a huge number of little snakes or eels, which I 
considered to be the fowl’s seed; as indeed it was. For 
the cock was more than half full-grown ;’ and I took it 
for certain that in squeezing out its dirt, I had compressed 
its seed-vessels so violently that I squeezed the material 
out of them too. Afterwards I squeezed the dirt out of 
the hind end of several young hens, but I didn’t discover 
anything but one living animalcule, which was about as 
big as a sixth of a blood-globule. The dirt consisted, 
further, of a clear matter, mixed with very many globules 
as big as a sixth of a blood-globule. These also looked as 
though they were composed of 2, 3, 4, 5, or 6 globules 
stuck together. And there were besides very many wee 
globules whereof 36 together (so I imagined) would be 
only as big as a blood-globule. 

I also” gently pressed the dirt out of two new-killed 
pigeons, that were about a month old; and in the first I 
couldn’t find any living animalcules at all. But in the 
dirt from the second pigeon (which was much clearer 
than the first’s) I saw many animalcules;* so that I 
judged there were quite 100 of ’em in a bit as big asa 
sand-grain. ‘These moved among one another very 
prettily *, and were all of one and the same bigness, 
having the figure of an egg, and being in my judgement 
as big as a sixth part of one of our blood-globules. 
Beyond this, the stuff was like what I have described 
above from hens. 

half volwassen MS. volwassen printed version. I follow the MS. 

because it is difficult to comprehend how the bird could have been “ more 
than full-grown’”’. The Latin translator evaded the ambiguity by calling 
the fowl “ major annis gallus’’. 

* ook MS. omitted from printed letter. 

* Bacteria of some sort, in all probability. 

* seer aerdig MS. but the Dutch printed letter says seer vaardig [| =very 
quickly] —which is concordantly rendered expeditissime in the Latin. 


The foregoing quotations—which contain, I believe, all 
that Leeuwenhoek ever wrote on such subjects—record a series 
of truly remarkable discoveries; and they prove conclusively 
that he discovered intestinal protozoa and bacteria in man 
and several other animals. He here saw, and recognizably 
described, the flagellate Giardia' and the Spirochaetes and 
other Bacteria in his own faeces. He also, I think, must have 
seen other human intestinal flagellates (possibly Trichomonas 
or Chilomastix), though this is uncertain: but he certainly 
saw bacteria in the excrement of a fowl and in that of a 
pigeon, though curiously enough he failed to find them in the 
dung of cattle and horses. 

Some of the interpretations which have been put upon 
Leeuwenhoek’s words in this connexion must be read to be 
believed. As I have commented upon them elsewhere’ I need 
say no more about them here. I will only note that the 
passages just quoted supply all the evidence there is for the 
statement—frequently met with in the  literature—that 
Leeuwenhoek described the ciliate Balantidium coli, and that 
he himself suffered from dysentery caused by this parasite. 
Beyond all doubt this is a literary fiction lacking all 
foundation. Though an Austrian nobleman® assures us 
that Leeuwenhoek could not have seen what he described, 
and therefore what he saw must have been something totally 
different ; and though a distinguished American medico‘* tells 
us that when Leeuwenhoek says he had weighed 160 lbs. for 
30 years and usually had solid stools, he meant that he had 
suffered from balantidial dysentery since the age of 30: never- 
theless, serious students of protozoology may well rest content 
with the plain and obvious meaning of his own simple words. 

Before we proceed to the next discoveries, it may not be 
amiss to emphasize the novelty of those just recorded. At the 
time when the foregoing observations were made, no protozoa 
or bacteria of any kind were known—except the free-living 

* Of. Dobell (1920). 

* Dobell (1920). 

* Stein (1867), Vol. II, p.321. Although I exposed Stein’s blunders 
some years ago, I note that a recent German writer (Pritze, 1928) still 
accepts them. But as he evidently overlooked my paper, and knows nothing 
of L.’s work, I cannot take his opinions seriously. 

* Strong (1904). 


forms described by Leeuwenhoek himself a few years earlier. 
No animal or “‘animalcule” smaller than a worm was known 
to live inside the body of man: and the existence of hordes of 
micro-organisms within the bodies of healthy animals was as 
wholly unsuspected as it was unheard-of. 

It is worthy of note, moreover, that neither here nor else- 
where in his writings does Leeuwenhoek associate entozoic 
protozoa or bacteria with the causation of disease. He found 
them in normal hosts, and it probably never occurred to him 
that any of them might have pathogenic properties. Having 
no medical education, and no preconceived notions regarding 
““animalcules,” he recorded his findings simply and objectively, 
and it was left to others to elaborate his great discovery into 
the vast present-day corpus of medical protozoology and 
bacteriology. In a sense, therefore, he missed the great 
practical implications of his revelation." But it must not be 
forgotten that the micro-organisms which he studied were all, 
in all probability, harmless; and consequently he deserves 
every credit for not speculating in excess of his facts. If 
every worker on the same subjects during the next 250 years 
had possessed an equally conservative and scientific spirit, a 
great deal of unnecessary confusion in our knowledge of 
“microbes ”’ might have been avoided. 

No further observations on entozoic protozoa were recorded 
until 1683. But in this year Leeuwenhoek wrote another 
highly interesting letter, in which he described many novel 
observations on frogs and other animals. He here accurately 
described, and discussed, the frog’s spermatozoa and _ blood- 
corpuscles—for the first time; and in the course of his 
description he interpolated an account of various “ animalcules ” 
which he had discovered incidentally. Some of these animal- 
cules were undoubtedly protozoa, but they are so involved 

* Contemporary medical workers, however, were not slow to seize upon 
the pathological possibilities of L.’s discoveries. For example we find, 
as early as 1683, that “the ingenious Fred. Slare M.D. and ¥.R.8.”, 
commenting upon a murren” in Switzerland which carried off many 
cattle, says: ‘I wish Mr. Leewenhoeck had been present at the dissections 
of these infected Animals, I am perswaded He would have discovered some 
strange Insect or other in them.”—Slare [alias Slear] (1647 ?-1727) was 
a physician and chemist. He qualified at Oxford in 1680, and became a 
Fellow of the Royal Society in the same year—just after L. himself. 

LETTER 88. 16 guLy 1683 931 

with the other matters mentioned that it is not always easy to 
separate them. The passages in question—omitting irrelevant 
details (duly indicated)—are as follows:! 

The first frog that I dissected sat in the road; and it 
seemed so weak from the cold,’ that though I gave it a 
bit of a kick on with my foot, it didn’t jump away. When 
I picked it up and opened it, I found ’twas a female, in 
whose guts there were worms, which had the shape of 
those worms that children void in their stools.’ These 
worms * were about as thick as a hair off one’s head.’ 

But what most surprised me was, that I observed in the 
blood (which had run out of the many blood-vessels that 
Thad cut, into the clean ° dish in which I dissected the frog) 
a great number of living animalcules,’ which were about 

" From Letter 38, 16 July 1683 [N.S.]. To Christopher Wren. 
MS.Roy.Soc. Read at a meeting of the Society held on July 18 [0.S.] — 
not on July 11, as appears (owing to omission of a date) in Birch, Vol. IV, 
p. 215. Published in Brieven, Vol. I (Dutch) ; Opera Omnia, Vol. I (Latin). 
The Dutch version first appeared in 1685 (Ontled. en Ontdekk.), and the 
first Latin version in the same year (Anat. et Contempl.). In both of these 
the letter is dated correctly : but in the Op. Omn. (and in the earlier Anat. 
s. Int. Rer. [1687], which contains a 2nd edition of the Latin letter) it is 
misdated July 26. A short English translation was published in Phil. 
Trans. (1683), Vol. XIII, No. 152, p. 347; and this was therefore the first 
version to appear in print. Hoole also translated a part of this letter, but 
not that which here concerns us. My translation is based primarily upon 
the original MS. 

* In a previous (untranslated) paragraph it is noted that these frogs 
were studied on 1 April 1683, when they were coupling. It is thus certain 
that the species was Rana temporaria—not R. esculenta, which breeds later. 

* Probably meaning Oxyuris (=Enterobius) vermicularis. 

“The “worms” found in this frog were obviously not protozoa or 
bacteria but nematodes; and— if the foregoing identification of Oxywris be 
correct—they were probably Ozysoma brevicaudatum, which is very 
common in R. temporaria. 

° A description of the blood-corpuscles of the frog is here omitted. 
° schone printed version. Not in MS. 

" When all the particulars related are taken into account—size, host, 
origin, movements, etc.—I think there can be very little doubt that this 
‘animalcule”’ was Trichomonas (or Trichomastia ?) batrachorum. 

‘A te ae 

” al 

s e 
i* Ww 




half as long and half as broad as one of the oval blood- 
corpuscles ; all being of one and the same structure. 
‘Twas no small pleasure to see this sight: for I had let 
so much time slip by, that the oval blood-corpuscles were 
sunk down somewhat (owing to their weight) towards the 
bottom, and then these animalcules made a pretty motion, 
for as they went a-swimming, they knocked into the 
blood-corpuscles, and sent them spinning. And I judged 
that in every particle of blood as big as asand-grain there 
were quite 50 animalcules. 

The blood aforesaid was very watery, and not pure 
blood by any means: for as soon as I separated a good 
bit of the frog’s skin from the flesh, some watery juice‘ 
began to run out of the skin, as well as the flesh ; and still 
more when I opened the belly. And as I had well-nigh 
bashed in the frog’s head, trying to make it keep quiet, 
methought some watery juice might well have been 
squashed out of its mouth or stomach too, and from this 
juice the animalcules might have come; for when I 
afterwards took blood out of the frog’s veins clean, I 
could discover no animalcules therein; neither when 
I viewed the watery matter which came from between the 
skin and the flesh, nor yet in that from the hollow of the 

In the foresaid watery matter, I noticed some irregular 
particles, most of which looked to me round, and were about 
as big as the globules of our blood. In some of these’ I 
could make out that they were composed of 6 lesser 
globules; and there were besides particles that seemed 
only about 4 of the bigness of the others. And when I 

* 4.¢., lymph. 

* From the foregoing and succeeding passages it is clear that L. satisfied 
himself that there were no animalcules in the blood or lymph: and 
consequently there is no foundation for the statement—sometimes made— 
that he discovered protozoa in the blood of the frog. 

* Plasma-cells, from the lymph. The smaller “ globules” inside them 
were doubtless the large basophile granules contained in such cells. 

" wl y 
dete Be 




From the engravings in the Dutch edition of Letter 38 (16 July 1683). X 13. 

Fig. A, Opalina (Cépédea) dimidiata. 
Fig. B, Nyctotherus cordiformis. 
Fig. C, a larval nematode ? 

facing p. 233 


examined the said watery blood of divers frogs, that had 
run out into the dish (for I took a clean dish for each 
several frog), a very few animalcules were‘ to be seen in 
it once more. 

Because I couldn’t satisfy myself about the animalcules 
aforesaid, though I was sure they didn’t belong to the 
blood itself, but were gotten into it by accident; in the 
month of June* I continued my observations, and at 
last I came across some frogs* in whose dirt, which I 
took out of the guts, I beheld an unconceivably great 
company of living animalcules, and these of divers sorts 
and sizes. ‘The biggest sort “ had the shape of Fig. A.2 Of 
these I judged there were quite 40 in a quantity of 
material as big as a grain of sand. ‘The second sort” had 
the figure of B: these were very fewinnumber. The third 
sort had very near the shape of our river-eels, as Fig. C: 
these were in even greater plenty than the first. And 
moreover the whole material was so full of little animal- 
cules, that the very dirt seemed to consist of nothing but 
little living animals; for the little particles of the dirt 
itself were so stirred’ by the motions of the animalcules, 
that they looked almost as though they were themselves 
animalcules too.© The number of the little animalcules 

* is MS.—corrected to zijn in printed version. 

> Anno 1683. 

* The species is not discoverable from this description, but the protozoa 
found indicate that they were Rana esculenta—not R. temporaria. lL. knew 
well (and could distinguish) both species. In Letter 65, 7 Sept. 1688, he 
tells us that there are two kinds of frog (vorsch) in Holland—the common 
“kikvorsch”’ [= R. temporaria], and the larger “ work” [= R. esculenta] 
which is “ eaten by the French.” 

* Opalina (Cépédea) dimidiata—without a doubt. 

> hadden de fig: van. A MS. hadden de gedaante van Fig. 3. A. printed 
version. See Plate XXIII. 

° Nyctotherus cordiformis : but see below. 

"wiert . . . bewogen MS.—corrected to wierden . . . bewogenin 

* This graphic description must appeal to every worker who has studied 
the intestinal protozoa of frogs, for it vividly describes the usual appearance 


last spoken of was so great, that I judged there were 
several thousand of ’em in every bit of matter as big as a 

On seeing this, I took it for certain that the animalcules 
which I said before were in the blood (which I had taken 
out of the dish), came to be there only in this way: 
namely, because the frog, when it was being cut up, 
voided its dirt into the dish, or because I had unwittingly 
wounded the guts of the frog, in whose dirt there must 

have been many animalcules, which got mixed with the 

It has been generally allowed that the larger animalcules 
which Leeuwenhoek here described and figured (his Figs. A 
and B) were ciliates—which occur so commonly in the guts 
of frogs. But it is possible, I believe, to identify them more 
exactly. To anybody familiar with the intestinal fauna of 
the two common frogs of Northern Europe (Rana temporaria 
and R. esculenta), it must be obvious that the abundant long 
organisms (Hig. A) were Opalina (Cépédea) dimidiata, while 
the smaller, scantier, and more rounded creature (Fig. B) was 
Nyctotherus cordiformis. Both of these occur very commonly 
in Lana esculenta, and I therefore infer that the frogs which 
Leeuwenhoek was studying on this occasion were of this 

It would have been impossible to determine the exact 
species of these ciliates before the intestinal protozoa of frogs 
had been adequately studied. Consequently, most of the early 
identifications are not worth serious consideration. The first 
correct determination we owe, I think, to Biitschli, who says 

of frogs’ faeces under the microscope. The “animalcules’”’ responsible for 
the phenomenon are flagellates (Trichomonas, Trichomastix, Chilomastiz, 
and Hexamuta), and various motile bacteria. 

" O. dimidiata is well known as the characteristic species of opalinid 
from this host: Nyctotherws, however, is usually described as occurring in 
i. temporaria only. That the above statement is correct I know from my 
own observations. 

* The frog in which L. found the worms previously was—as already 
noted—f. temporaria: but there is nothing in his words to prove that the 
frogs of the second batch were not of the other species. If they were, then 
the above identification amounts almost to a certainty. 


that in Leeuwenhoek’s description “ Opalinae and Nyctotherus 
can be recognized with sufficient certainty.”* No species are 
indicated, though the two which I have mentioned must, I 
think, have been intended. Saville Kent, however, had 
previously identified Leeuwenhoek’s Fig. A as Opalina 
intestinalis :” but this is highly improbable, because there is 
no certain record of this species having ever been found in 
either R. temporaria or R. esculenta.’ 

Metcalf, who has studied the Opalinidae in greater detail 
than any other specialist, writes of Leeuwenhoek’s observations 
as follows : * 

‘“ Opalina was first mentioned [?] by Leeuwenhoek in 
1685° [?]. In his Opera omnia (1722) he quotes the earlier 
record [?] of finding innumerable animalculae [sic] of 
various sizes and forms in the foeces [sic] of the frog. One 
of these figured [L.’s Fig. B] seems in all probability to have 
been O. ranarum. Another may have been O. dimidiata 
DRG ya cates. diag 

From this it seems to me that Metcalf cannot have studied 
Leeuwenhoek’s works or words very carefully, nor does he 
- appear to appreciate the difficulties of his own interpretation. 
If—as he suggests, and as I am convinced—Fig. A represents 
O. dimidiata, then the smaller rounded form (Fig. B) can 
hardly have been O. ranarum. For this species is at least as 
large as O. dimidiata, and occurs typically in a different host— 
RR. temporaria.” Consequently, if Metcalf’s interpretation 
were correct, it would leave the small size of Fig. B un- 

' Biitschli (1887-89), Vol. III, p. 1101. The date of the observations is 
wrongly given, however, as 1687. Cf. also zbzd., pp. 1718 and 1721. 

* Kent (1881-82), Vol. II, p. 562. 

* Opalina (Protoopalina) intestinalis is a species proper to Bombinator— 
not Rana. Cf. Metcalf (1923), p. 51. Kent’s error was first noted by 
Metcalf (1909), p. 319. 

* Metcalf (1909), p. 319. My comments are interpolated in square 
brackets for the sake of brevity. In my opinion this single sentence 
contains at least six mistakes, but it seems unnecessary to do more than 
indicate them. 

° In a later work (Metcalf, 1923, p. 438) the date is given as 1865 [! ]— 
presumably by misprint of the first date (1685), which was itself incorrect. 
Little errors of this sort abound in nearly all discussions of L.’s work. 

° I know of no certain record of O. ranarwm having been found in R. 
esculenta, or of O. dimidiata from R. temporaria. Cf. also Metcalf (1923). 


explained, and would necessitate the assumption that 
Leeuwenhoek found his ciliates not merely in two different 
frogs, but in frogs of two different species—of which there is 
no indication whatever in his own writings. But if, on the 
other hand, it be agreed that Fig. A shows O. dimidiata, then 
the frog was a specimen of R. esculenta, and the smaller ciliate 
was Clearly Nyctotherus—not an opalinid at all. The figure 
certainly suggests this strongly, and everything else supports 
this obvious, natural, and easy interpretation. 

When we come to consider Leeuwenhoek’s Fig. C, however, 
we are faced with very grave difficulties. This organisin is 
said to have been like a “‘ river-eel ”’, and to have been abundant 
in the frog’s faeces: and in size it appears, from the figure, to 
have been longer than a Nyctotherus—though the drawings 
were not made accurately to scale. Elsewhere in Leeuwen- 
hoek’s writings we find nematodes (Anguillula, etc.), spirilla, 
and spirochaetes, all likened to “eels”: and in the rectal 
contents of . esculenta we may find not only various species 
of nematodes, spirilla, and spirochaetes, but also long flexible 
and actively motile bacilli (Bacillus flexilis and similar forms). 
To determine which—if any—of these Leeuwenhoek may have 
seen on this occasion, is I think impossible. I must therefore 
leave Fig. C unidentified, though I am inclined to believe that 
it depicts a larval nematode. 

I conclude, consequently, that Leeuwenhoek discovered 
and described Opalina, Nyctotherus, and Trichomonas (or 
Trichomastix) in the faeces of frogs, in addition to various other 
protozoa and bacteria which are not now identifiable.’ 

And now we come to a letter which is, perhaps, as famous 
as any Leeuwenhoek ever wrote to the Royal Society—the 
one containing his account of the ‘‘ animalcules”’ in the human 
mouth. This letter is frequently quoted—or rather mis- 

" For example, there is a definite indication of the mouth, and the 
outline is—to me—quite convincing. The interpretation of Fig. B as 
Balantidium coli—recently put forward by Pritze (1928)—is so outrageous 
as to deserve no further notice. 

* I ought perhaps to point out that Prowazek (1913) has identified some 
of these organisms with Balantidiwm coli. Although he has been copied by 
others (e.g. Pritze, 1928), his interpretation is manifestly absurd. There is 
no evidence that L. ever saw any species of Balantidiwm in the frog, and 
B. colt certainly does not live in this host. 


quoted—by bacteriologists, and is usually said to be the first 
memoir in which bacteria of any sort are mentioned. How 
far this 1s true, readers of foregoing quotations can judge for 
themselves. References to this important epistle, addressed 
to Francis Aston, Sec.R.S.," are almost invariably given 
incompletely or incorrectly ; and this is doubtless due in 
part—though not altogether—to the fact that many versions 
of it are extant. Moreover, many different interpretations of 
the organisms described have been advanced, and this has led 
to some truly astonishing conclusions. Yet Leeuwenhoek’s 
words are, as usual, plain and straightforward, while the 
interpretation of his observations appears to me obvious. To 
anybody familiar with the flora and fauna of the human 
mouth they surely present no difficulties. I shall therefore 
give his own words (as well as I can) first, and shall comment 
upon them afterwards—adding exact references but ignor- 
ing many manifestly absurd statements made by other 
The passages in question run as follows: ? 

* Concerning Francis Aston little is now known. (He is not mentioned 
in the Dict. Nat. Biogr.) He was elected F.R.S. in 1678, and became 
Secretary in 1681—a post which he suddenly threw up in 1685 (ef. Rec. 
Roy. Soc., and Weld, I, 302). Afterwards he received a gratuity from the 
Society (Weld, I, 305), and on his death bequeathed to them his estate at 
Mablethorpe in Lincolnshire, together with his books and instruments 
(Weld, I, 428). His portrait now hangs in the apartments of the Society 
at Burlington House (at the foot of the staircase). For the following 
additional information I am indebted to Mr H. W. Robinson, Assistant 
Librarian of the Royal Society: Aston was born about 1644, and died in 
June or July 1715. He went to Westminster School in 1656, and was 
King’s Scholar in 1660 (aged 16). He entered Trinity College, Cambridge, 
in 1661, and became Fellow in 1667. (B.A. Cant. 1664/5: M.A. 1668.) 
He travelled abroad for some years, and in his youth was an intimate friend 
of Isaac Newton. 

* From Letter 39. 17 September 1683. To F. Aston. MS.Roy.Soc. 
Published in Brieven, Vol. I (Dutch), and Opera Omnia, Vol. II (Latin). 
The Dutch version was first printed in 1684 (Ondervind. en Beschouww. 
pp. 1-19), the Latin in 1695 (Arc. Nat. Det. pp. 41-53). Both versions are 
wrongly dated the 72th of the month (‘‘ den 12 Septemb. 1683” and “ pridie 
Iduum Septembris 1683”) apparently through a misreading of the MS. 
Owing, it would seem, to some oversight, two different English abstracts 
appeared in the Plil. Trans. The first was published in Vol. XIV (1684), 
No. 159, p. 568 [b¢s—a misprint for 598]: the second in Vol. XVII (1693), 
No. 197, p. 646. [The first—published 20 May 1684—is the fuller and 
better.] Hoole (1798) has given a third—and as far as it goes the best— 


I have ere this sent you my observations concerning 
spittle, which I see have been made public in print in the 
Lectures and Collections published by Mr. Robert Hooke, 
Secretary of the Roy. Soc., in the year 1678.’ Since 
that time I have made divers further observations on 
my spittle, with the idea that if there be any animalcules 
lying about in the body, they would get into the mouth, 
sooner or later, through the spit-ducts; but in what 
observations I made to this end, I could make out no 
animalcules there, nor could I say aught else but what 
I have hitherto writ. 

"Tis my wont of a morning to rub my teeth with salt, 
and then swill my mouth out with water: and often, 
after eating, to clean my back teeth with a toothpick, as 
well as rubbing them hard with a cloth: wherefore my 
teeth, back and front, remain as clean and white as falleth 
to the lot of few men* of my years,’ and my gums (no 

partial English translation in Select Works, Vol. I, p. 118. Léffler (1887, 
p. 5) has translated a fragment into German, but he misdates the letter 
September 14. It was read at a meeting of the Society held on 24 October 
1683 [O.S.]: ef. Birch, Vol. IV, p. 219. Various reproductions of the 
illustrative figures are noted below (p. 244 et seq.). They have already 
given rise to much confusion and misstatement.—-Though there are already 
at least one Dutch, two Latin, and three English versions of this letter in 
print, I rely upon the original MS. (in L.’s own hand), from which my 
translation has been made. 

"A reference to Letter 23, 14 January 1678. To R. Hooke. 
MS.Roy.Soc. English version (incomplete) published in Hooke’s Lect. & 
Collect. (1678), part II, Letter 2, p. 84. (Reprinted in Hooke’s Lect. Cutl. 
(1679) pt. V.)—This letter contains an account of certain ‘‘ Globules in the 
Flegm’’: but L. had examined saliva still earlier, for in Letter 4 (1 June 
1674, to Oldenburg) he notes that ‘‘In clean spit, examined by me in the 
morning, I find a few very little particles floating in the liquid; whereof 
I saw some sink to the bottom; as also divers irregular particles, some of 
which seemed to consist of globules stuck together. And in the spittle that 
I examined in the afternoon, I found the globules and irregular particles in 
greater plenty”. (MS.Roy.Soc. Partial English translation in Phil. Trans. 
(1674), Vol. IX, No. 106, p. 121.) 

* als er weijnig menschen van mijn Jaren sign MS. als weynig 
menschen . . . gebeurt printed version. 

* When he wrote this, L. was approaching his 51st birthday. He tells 

ey Mi 
iy Tf 

is Me 

j 4 i pean i 
Woathy o ih a re 

1 Kt ae ta 

cr a | 
Nunet _ a 

; i Ay R) 
Oh yent TA af ii i at 


if a 

* ng ae oe 

, ay AS No is ay my) ia A 

a i ani on 
nn oe ee oe er a ice ; ke ts 

nag a ele Pea Al) 

ua ea mn es ay 

a ie ‘ is 


(Letter 39, 17 Sept. 1683) 
Enlarged (X 13) from the engravings published in Arc. Nat. Det., 1695. 

Fig. A, a motile Bacillus. 

Fig. B, Selenomonas sputigena. C....D, the path of its motion. 

Fig. E, Micrococci. 

Fig. F, Leptothrix buccalis. 

Fig. G, A spirocheete—probably “ Spirochaeta buccalis,” the largest form found 
in this situation. 

facing p. 239 

LETTER 39. 17 SEPTEMBER 1683 939 

matter how hard the salt be that I rub them with) never 
start bleeding. Yet notwithstanding, my teeth are not 
so cleaned thereby, but what there sticketh or groweth 
between some of my front ones and my grinders (whenever 
I inspected them with a magnifying mirror), a little 
white matter, which is as thick as if ’twere batter.” On 
examining this, I judged (albeit I could discern nought 
a-moving in it) that there yet were living animalcules 
therein. I have therefore mixed it, at divers times, with 
clean rain-water (in which there were no animalcules), 
and also with spittle, that I took out of my mouth, after 
ridding it of air-bubbles (lest the bubbles should make 
any motion in the spittle): and I then most always saw, 
with great wonder, that in the said matter there were 
many very little living* animalcules, very prettily 
a-moving. The biggest sort had the shape of Fig. A* 
[Plate XXIV]: these had a very strong and swift 
motion, and shot through the water (or spittle) like a 
pike * does through the water. ‘These were most always 
few in number. 

The second sort had the shape of Fig. B. These oft- 
times spun round like a top, and every now and then 
took a course like that shown between C and D: and 
these were far more in number. 

us elsewhere, however, that he sometimes suffered from toothache—to 
alleviate which he smoked a pipe of tobacco, which generally made him 
feel very sick. He also tells us later how some of his teeth decayed. 

‘ Nogtans printed version—omitted in MS. 

* beslagen meel MS. and Dutch printed version “wetted flower” Phil. 
Trans. (1684) “like a mixture of flour and water” Hoole farinae aqua 
subactae similem Latin edition. The 2nd Phil. Trans. version (1693) 
incorrectly calls this soft mealy material (materia alba) ‘‘a kind of gritty 

* levende is here in the MS. but not in the printed version. 

* hadde de Fig: van A. MS. was van de Fig: A. printed version. 

® een snoek MS. and Dutch printed version. The Latin translator 
rendered this—with some justification—piscis lupus: which caused Loffler 
(1887, p. 5) to mistranslate it ‘‘ Rauwbfisch” (instead of Hecht). To “ shoot 
through the water like a pike” is a phrase commonly used by L. to describe 
any rapidly darting aquatic animalcule. 






To the third sort I could assign no figure: for at times 
they seemed to be oblong, while anon they looked 
perfectly * round. ‘These were so small that I could see 
them no bigger than Fig. HK: yet therewithal they went 
ahead so nimbly, and hovered so together, that you might 
imagine them to be a big swarm of gnats or flies, flying in 
and out among one another. ‘These last seemed to me 
e’en as if there were, in my judgement, several thousand 
of ’em in an amount of water or spittle (mixed with the 
matter aforesaid) no bigger than a sand-grain; albeit 
there were” quite nine parts of water, or spittle, to one 
part of the matter that I took from betwixt my front 
teeth, or my grinders. 

Furthermore, the most part of this matter consisted of 
a huge number of little streaks, some greatly differing 
from others in their length, but of one and the same thick- 
ness withal; one being bent crooked, another straight, 
like Fig. F, and which lay disorderly ravelled together. 
And because I had formerly seen, in water, live animal- 
cules that had the same figure, I did make every 
endeavour to see if there was any life in them; but 
I could make out not the least motion, that looked lke 
anything alive, in any of ’em. 

I have also taken spittle from the mouths of two 
different womenfolk,’ that I’m sure clean their teeth 
every day, and examined it as narrowly as I was able to, 
but could discern therein no living animalcules. But 
afterwards I examined the same spittle mingled with 
a little of the matter that I picked out with a needle from 
betwixt their teeth : and then I discovered as many living 

volkomen is here in the printed text, but not in the manuscript. 
was MS.—corrected to waren in print. 

twee distincte Vrouwspersonen MS. and Dutch ed. binaruwm foeminarum 
5 ce ? 
ed. ‘‘two several women” Phil. Trans. (1684) other Persons ”’ 

Phil. Trans. (1693) “‘ two ladies’ Hoole (1798). It is almost certain that 
these were L.’s own womenfolk—his second wife Cornelia, and his daughter 


Cle odo eve Len Soe bch WI & he oars on gel , Lu 
Sohoefen gree hi rterater po fission ocses 
AD Chex fo DEN TS 
feos Sot Oe why an a WEA 
Ee je re meh C. em D. tf atm poweden \' Soke learner 
Creel am cerder amt geht. Jhon de: (eDe Srost- Poul Mat 

~~, Seo clin LOB spew) eno De ander 
4 ne A ‘a - ele Date! binerce Soe Ze. oat 
eh eleles & age cee LeQe devi eee ha E. mat 

ew eer. Cae he far So 
ea, cr a Astin’ "Nets nna shp 

hwel te Gerren men { dat-iL cordece cen 
Soi ER te ry ae 
(Oem x amet Ve ie 5% of peed 

Rae Asem Shevere 

ettte rmatene Ky etn over 
ae ye abe. (GEL (ee ies. Klidentre Cle phi ouwe +5 aD 

4, ogtang Comm Lon ade Deh. =: ibe Scull 
Vie tier te mete Bk cpt Py Fs ange, 
ro es SMES SP ie we ao 
wwe Dea oak ee ington Tae Laven Seb leo 
aii 4! Aaildesin se Ae heb 1k, atte (Qeserreny : oon Blond — pO 
"£3 S Bic ph de ae VWogex m cai On aor ik heb 9 eeu 

Peuwregr, aft rie gf there: gelek , ja ay~ 
ys Anan 4 < an J f ‘2 sy o d nti 
(17 Sept. 1683: leaf 2 recto = page 8), 
containing part of Leeuwenhoek’s description of the Bacteria in the mouth. 
Facsimile. (The first word is [desel] ve, continued from the previous page.) 
This is a good sample of Leeuwenhoek’s handwriting at this period. 

facing p. 240 

ee CA rey aU Pep me MUN ee emt es et ee 
“oy eiy : ih NI. 3 aie va ne ay OL Pa iy bik 
ay ve halt Bs Wb eee See “3 kk 4 Py Tue J) Md " rr ~ 

op ee aad ne 
% tee, caNT eo 
; a i he ; hid Bh . i tor ae a oy re : we - o i 
Farben me ii me! ata: GIN apt! 

Ccemauenen ett par pers 
ae Ce ae me mag 

yey i 

ae . re tan 7 ee 

a Le te, 5 date} 
A} rca! weer; agit) See a 2: =e 5 tf \ Atel rie 

sie a eh Pith ene + es 

‘ he | wee 

77° Sey 
o seca) Sie As 
tant 7 \ P), oy Hye Em 
. 7 ’ 
aA Wiki te c g } 
7 i be | i 
t vans ask 
it: ey - ‘aye a i 
h 4 8 is 
eo 14 
ee eee 

Poe ie presge af 
an te i 2 ru a yeu! 

: - wi f 

ae Ht » i, ~* aie ; , ; : ~ a 

al hoe el i ona 

7 ee 77 h 
ae ee 
7 ager be 
Disa ie} iikennk 1h 

| any ah a _ yids: ah 

a % ‘ ans Aas i waka 
ke ~~ va ie 

oa An oN oN 

ton - ie 

i ea i 

i. yor ile 

ay haere i 


animalcules, together with the long particles, as herein- 
before related. 

I have also examined the spittle of a child about eight 
years old, and likewise could discover no living animalcules 
therein ; and afterwards the same spittle, mixed with the 
stuff that I got out from atween the child’s teeth: where- 
upon I perceived as great a many animalcules and other 
particles as heretofore made mention of. 

I didn’t clean my teeth (on purpose) for three days 
running, and then took the stuff that had lodged in very 
small quantity on the gums above my front teeth; and I 
mixt it both with spit and with fair rain-water;* and 
I found a few living animalcules in it too. 

While I was talking to an old man (who leads a sober 
life, and never drinks brandy or tobacco,’ and very seldom 
any wine), my eye fell upon his teeth, which were 
all coated over; so I asked him when he had last cleaned 
his mouth? And IJ got for answer that he’d never washed 
his mouth in all his life.” So I took some spittle out of 
his mouth and examined it; but I could find in it nought 
but what I had found in my own and other people’s. I 
also took some of the matter that was lodged between and 
against his teeth, and mixing it with his own spit, and also 
with fair water (in which there were no animalcules), I 
found an unbelievably great company of living animalcules, 
a-swimming more nimbly than any I had ever seen up to 
this time. The biggest sort (whereof there were a great 
plenty) bent their body into curves in going forwards, as 
in Fig. G. Moreover, the other animalcules were in such 
enormous numbers, that all the water (notwithstanding 

' water MS. vregen-water Dutch printed version. 
2 In olden times it was customary to speak of “ drinking” tobacco— 

both in Holland and in England—though it meant “ smoking ” (as we now 

* Hoole (1798, p. 119)—with his usual squeamishness—purifies these 

coarse details into more polite observations upon “ the teeth of an old 
gentleman, who was very careless about keeping them clean. 





only a very little of the matter taken from between the 
teeth was mingled with it) seemed to be alive. The long 
particles too, as before described, were also in great 

I have also taken the spittle, and the white matter that 
was lodged upon and betwixt the teeth, from an old man’ 
who makes a practice of drinking brandy every morning, 
and wine and tobacco in the afternoon; wondering 
whether the animalcules, with such continual boozing, 
could e’en remain alive. I judged that this man, because 
his teeth were so uncommon foul,’ never washed his 
mouth. So I asked him, and got for answer: ‘‘ Never 
in my life with water, but it gets a good swill with wine 
or brandy every day.” Yet I couldn’t find anything 
beyond the ordinary in his spittle. I also mixed his spit 
with the stuff that coated his front teeth, but could make 
out nothing in it save very few of the least sort of living 
animalcules hereinbefore described time and again. But 
in the stuff I had hauled out from between his front teeth 
(for the old chap hadn’t a back tooth in his head), I made 
out many more little animalcules, comprising two of the 
littlest sort. 

Furthermore, I put some strong wine-vinegar in my 
own mouth, and then set my teeth, and let the vinegar run 
betwixt ’em time after time: and after doing so, I rinsed 
my mouth out thrice with fair water. Afterwards I once 
more fetched out some of the foresaid stuff from between 
my front teeth, as well as from between my grinders ; 
and I mixed it divers times both with spittle and with 
clean rain-water: and most always I discovered in it 
an unbelievable number of living animalcules, though most 
of ’em were in the matter I got from between my back 
teeth, and only a few had the appearance of Fig. A. 


Hoole (1798) prudishly refrained from translating the observations 

made upon this disreputable ‘old gentleman”’, who, in the Phil. Trans. 

(1684), is called simply—without other descriptive detail—" a good fellow ”. 


2 ongemeen vurjl MS. buyten gemeen vuyl printed letter. 



I have also put a little wine-vinegar to this stuff mixed 
with spittle, or with water: whereupon the animalcules 
fell dead forthwith. And from this I drew the conclusion 
that the vinegar, when I filled my mouth with it, didn’t 
penetrate through all the matter that is firmly lodged 
between the front teeth, or the grinders, and killed only 
those animalcules that were in the outermost parts of 
the white matter. 

In several of the observations aforesaid, I saw on 2 or 
3 occasions some very bright transparent particles, 
whereof many were perfectly round, others having an 
irregular round figure. ‘These were of divers bignesses, 
and the biggest of them I judged to be about 25 times 
bigger than a globule of one’s blood’: and if they hadn’t 
sunk to the bottom, by reason of their weight, I should 
have taken them for fat-particles.’ 

I have had several gentlewomen in my house, who 
were keen on seeing the little eels in vinegar: but some 
of ’em were so disgusted at the spectacle, that they vowed 
they’d ne’er use vinegar again. But what if one should 
tell such people in future that there are more animals 
living in the scum on the teeth in a man’s mouth, than 
there are men in a whole kingdom ? especially in those 
who don’t ever clean their teeth, whereby such a stench 
comes from the mouth of many of ’em, that you can 
scarce bear to talk to them; which is called by many 
people “ having a stinking breath”, though in sooth ’tis 
most always a stinking mouth. For my part I judge, from 
myself (howbeit I clean my mouth like I’ve already said), 
that all the people living in our United Netherlands are 
not as many as the living animals that I carry in my 
own mouth this very day: for I noticed one of my back 
teeth, up against the gum, was coated with the said matter 

z.e., they had about thrice the diameter of a human red blood-corpuscle. 

These were probably squamous cells—the smaller being “salivary 
corpuscles ” (dead leucocytes). 


vet-deeltgens ; 2.e., oil droplets. 


for about the width of a horse-hair, where, to all appear- 
ance, it had not been scoured by the salt for a few days ; * 
and there were such an enormous number of living 
animalcules here, that I imagined I could see a good 1000 
of ’em in a quantity of this material that was no bigger 
than a hundredth part of a sand-grain.’ 

It must be noted here that the illustrations accompanying 
the foregoing letter differ slightly in each version. The 
original drawings are, unfortunately, lost: and the_ best 
figures—those now reproduced—are in the original Latin 
edition (Arc. Nat. Det., 1695) and Opera Omnia. From the 
first Dutch edition® (1684) Fig. G, a highly important 
picture, was for some unexplained reason omitted altogether." 
In the first Phil. Trans. version (1684) all the figures appear, 
but Fig. G has an irregular and unrecognizable shape: while 
in the second Phil. Trans. version (1693) Fig. G again 
disappears, and the others are reversed.’ 

A plausible explanation of these discrepancies is the 
following. The figures originally sent by Leeuwenhoek to the 
Royal Society were badly drawn and poorly engraved, and he 
was probably dissatisfied with them—especially with Fig. G, 
which was very bad. When he was about to publish the 
same pictures himself later in the same year, he resolved to 
have this figure redrawn, and therefore told the engraver not 
to copy the original. Then, by an oversight, the letter was 
printed with the figure missing. later, discovering his 
mistake, Leeuwenhoek had a new and improved drawing 

’ The Latin version inserts here ‘‘ materiam illam inde exemi’’ [=so I 
extracted some of this stuff], but this is not in the Dutch originals. 

2 The sentences in the foregoing paragraph are loosely strung together 
and ungrammatical in the original: and consequently they are not easy to 
translate into intelligible English without “ improving ’’ beyond recognition. 
If the reader should find my version inelegant and confused, I would refer 
him to its prototype—which is much worse. 

® In the only copy of the 2nd Dutch edition of L.’s works which I have 
yet seen, the whole letter containing these observations (No. 39) is 
missing—the copy being otherwise perfect. 

* It is referred to, however, in the text (both MS. and printed Dutch 

’ This is obviously due to the engraver’s direct copying of the original 
drawings on to his plate. 


prepared, and this was inserted in the Latin translation which 
appeared subsequently. The still later omission of Fig. G 
from the second Phil. Trans. version was probably merely a 
consequence of the great condensation which this very short 
and faulty translation underwent at the hands of its editors. 

Some such explanation would readily account for the 
variations in the different versions. But in any case, I think, 
we need not hesitate to accept the final and complete set of 
drawings published with the Latin letter—drawings which 
Leeuwenhoek must himself have seen and passed for press. 
The omission of Fig. G from the Dutch edition was certainly 
unintentional, as it is referred to in the letterpress. 

It is not possible to doubt, after reading the foregoing 
descriptions and inspecting the pictures, that Leeuwenhoek 
discovered ‘the bacteria in the human mouth: for he described 
—and described recognizably—all the most characteristic 
forms occurring in this situation. To anybody familiar with 
these organisms his figures speak so clearly that his words are 
almost superfluous. If I were shown these sketches for the 
first time, and asked to interpret them, I should be able to 
say—after only a moment’s reflexion—what they probably 
depict. Fig. A is a Bacillus: Fig. B shows the peculiar 
organism known as “ Spirillum sputigenum” :° Fig. EK shows 
some of the Micrococct commonly present in the mouth: Fig. 

"IT must note that priority for this discovery has been claimed for 
Hartsoeker: but this is due to a misunderstanding. The true story can 
be pieced together from L.’s writings and Hartsoeker’s own words (1730). 
Hartsoeker, knowing of L.’s discovery of the spermatozoa, tried to pass it 
off as his own: but he says that he was ashamed to tell people that he had 
examined semen with the microscope, and therefore told them at first that 
the “ animalcules’’ which he had found in it were in the saliva. But he 
further says, quite definitely (1730, p. 6), that he never really saw any 
animalcules in saliva, and he attempts to discredit L.’s discovery. He 
regarded it as an invention. Consequently, Hartsoeker himself never 
claimed to have found any organisms in the human mouth, and even 
denied their existence. 

2 So named by Miller (1890). This organism is not really a Spirillwm 
at all, but belongs to the genus Selenomonas Prowazek, 1913a. I have 
studied it (in pure culture) but I have seen no accurate description of it.— 
In the genus Selenomonas the flagella arise from the concave surface of the 
arched or crescentic body—not from its ends, as in Spirillum. Their 
lashing produces the curious whirling motion observed by L. Although the 
text-books of bacteriology are usually silent on the subject, I can say from 
my own knowledge that Selenomonas sputigena is very common in human 
mouths—and very difficult to isolate in cultures. 


F is the Leptothriz’* always found on the human teeth: and 
Fig. G is unquestionably a spirochaete—probably the so-called 
“ Spirochaeta buccalis”.” The figures obviously represent 
bacteria, and include no protozoa; and nowhere but in the 
mouth is such an assemblage of forms to be found. When 
Leeuwenhoek’s own words are considered in conjunction with 
these illustrations, the interpretations just advanced must 
surely be self-evident to everybody who studies the microbes 
of the human mouth “ with the help of a good microscope.” 

Yet ever since the foregoing observations were recorded 
they have been misinterpreted—and even questioned and 
denied—in the most astonishing manner. It is unnecessary 
to chronicle here all the wild assertions that have been made 
in this connexion.’ 'T'wo of the most recent comments will 
serve as illustration : 

(i) Singer (1914) reproduces the figures from the Phil. 
Trans. 1684 (misdated by him 1683), and says that figs. A, F, 
and G [the spirochaete] are all ‘‘rod-shaped organisms ”’ 
[meaning bacilli?]; and that B [Selenomonas| is “a flagellated 
organism” [meaning a protozoon?]|. He even recognizes 
‘ sarcinae’”’ in Leeuwenhoek’s description: but the figure * so 
strangely interpreted is said by Leeuwenhoek himself to 
represent epidermal scales from the human skin, as seen 
under a low magnification. 

(ii) Wenyon (1926), discussing the Trichomonas of the 
human mouth, says “it is probable that Leeuwenhoek saw 
the flagellate in the tartar of his own and other people’s 
teeth.”°’ Although no reference is given to the passage in 

' Leptothrix buccalis Robin, 1853: Bacillus maximus buccalis Miller, 
| 7 specific designation commonly ascribed to Cohn. But see Dobell 

* I must mention, however, that Robin (1853, pp. 352-354) made a 
careful study of the Latin versions of Letter 39, and correctly identified the 
Leptothrix. Ue also recognized Fig. B as a “vibrion”’. Beijerinck (1913, 
p. 10, note) wrongly supposes that Ldéffler (1887) was the first to direct 
attention to L.’s pictures of bacteria in the human mouth. 

* Fig. H—which occurs in the same letter, but is not reproduced here. 
To my mind this figure bears no resemblance to a Sarcina or any other 
bacterium : and of course no Sarcina lives normally in the mouth of man. 

° Wenyon (1926), Vol. I, p. 656. So far as I am aware, there is no 
passage in any of L.’s writings which can be plausibly interpreted as an 
account of the Trichomonas of the human mouth. 


which T'richomonas is supposed to have been described, it is 
clear that Wenyon must here refer to one or other of the 
“animalcules’’ which we have just discussed—but which 
one, I cannot even guess. To me it is obvious that they were 
all bacteria: but Wenyon takes the view that none of them 
could have been, since he considers that bacteria ‘“‘ were quite 
beyond the scope of the simple magnifying apparatus used by 
Leeuwenhoek.” ? 

Thus, while Singer finds, in Leeuwenhoek’s words and 
pictures, more bacteria than Leeuwenhoek himself, Wenyon is 
able to recognize none at all! 

Some further researches on the ‘“animalcules” in the 
human mouth were reported by Leeuwenhoek nine years 
later. His letter runs as follows: ? 

In my letter of the 12th* of September, 1683, I spake, 
among other things, of the living creatures that are in 
the white matter which lieth, or groweth, betwixt or 
upon one’s front teeth or one’s grinders. Since that 
time, and especially in the last two or three years, I have 
examined this stuff divers times; but to my surprise, I 
could discern no living creatures in it. 

1 Wenyon (1926), p. 3. 

2 From Letter 75. 16 September 1692. To the Royal Society. 
MS.Roy.Soc. Printed in full in Brieven, Vol. II, p. 508: Opera Omnia, 
Vol. II, p. 307 (1st pagination). The Dutch version first appeared in 1693 
(Derde Vervolg d. Brieven), the Latin in 1695 (Arc. Nat. Det., p. 334). No 
English translation was ever published in the Phil. Trans., and so far as I 
am aware no English version has yet appeared in print. (Hoole did not 
translate the relevant passages in this letter.) A German paraphrase—of a 
fragment only—is given by Léftler (1887, p. 6), who misdates the epistle 
October 1.—The printed Dutch version follows the original MS. so closely 
that few annotations are necessary : while the Latin version in Opera Omnia 
(ed. noviss., 1722)—by an unknown hand—is one of the best translations I 
have ever read. Barring a few trivial misprints, it renders its Dutch 
prototype with wonderful faithfulness.—The originals of the illustrations 
are lost ; the MS. in the Roy.Soc. collection being accompanied by a proof 
of the engraved plate sent by L. himself in place of the original sketches. 

* As noted already (p. 237, note 2), the correct date of this letter— 
as written by L. himself on the MS.—is not the 12th but the 17th of 



Being unable to satisfy myself about this, I made up 
my mind to put my back into the job, and to look into 
the question as carefully as I could. But because I keep 
my teeth uncommon clean, rubbing them with salt every 
morning, and after meals generally picking them with a 
fowl’s quill, or pen; I therefore found very little of the said 
stuff stuck on the outside of my front teeth: and in what 
I got out from between them, I could find nothing with 
life in it. Thereupon I took a little of the stuff that was 
on my frontmost grinders; but though I had two or 
three shots at these observations, ’twas not till the third 
attempt that I saw one or two live animalcules. Yet I 
could well make out some particles lying about that I 
felt sure must have been animalcules. This put me in a 
quandary again, seeing that at and about the time when 
I wrote to you concerning these animalcules, I never 
failed to see there was life in them: but though now I 
used just the very same magnifying-glass and apparatus 
(which I judged to be that best suited to the purpose), 
yet I couldn’t make out any living creatures at all. 

Having allowed my speculations to run on this subject 
for some time, methinks I have now got to the bottom 
of the dying-off of these animalcules. The reason is, I 
mostly or pretty near always of a morning drink coffee, 
as hot as I can, so hot that it puts me into a sweat: 
beyond this I seldom drink anything save at mealtimes 
in the middle of the day and in the evening; and by 
doing so, I find myself in the best of health. Now the 
animalcules that are in the white matter on the front- 
teeth, and on the foremost of the back-teeth, being unable 
to bear the hotness of the coffee, are thereby killed: like 
I’ve often shown that the animalcules which are in water 
are made to die by a slight heating. 

Accordingly, I took (with the help of a magnifying 
mirror) the stuff from off and from between the teeth 
further back in my mouth, where the heat of the coffee 
couldn’t get at it. This stuff I mixt with a little spit 
out of my mouth (in which there were no air-bubbles), 

LETTER 75. 16 SEPTEMBER 1692 249 

and I did all this in the way I’ve always done: and then 
I saw, with as great a wonderment as ever before, an 
unconceivably great number of little animalcules, and 
in so unbelievably small a quantity of the foresaid stuff, 
that those who didn’t see it with their own eyes could 
scarce credit it. These animalcules, or most all of them, 
moved so nimbly among one another, that the whole stuff 
seemed alive and a-moving. 

I again paid the strictest attention I possibly could to 
the bigness, or at any rate to the length, of the bodies of 
many of ’em'; but mostly to the little animalcules, which 
looked to me roundish. Afterwards, I took a grain of 
coarse sand (of the sort of sand that we use here in this 
country* for scouring the pewter, and other household 
chattels), and I stuck this sand-grain in front of the 
microscope through which I had seen the animalcules : 
and I am bound to say, after making careful measure- 
ments, which I did by eye, that the diameter of the sand- 
grain was above a thousand times longer than the diameter 
of one of the little animalcules which I saw in great 
numbers. Consequently, then, such a grain of sand was 
far more than a thousand millionfold bigger than one of 
the little creatures aforesaid. 

Besides, I also saw divers animalcules * whose bodies 
were a bit thicker than the little animals hereinbefore 
spoken of; but these were quite 5 or 6 times longer than 
they were thick, and therewithal their body was of equal 
thickness all along, so that I couldn’t make out which 
was their head, or which their tail end; all the more 
because when they were a-swimming, which they did 
very leisurely (and this was their only motion, with a 
little bending of the body now and then, as it seemed to 
me), they would go ahead first with one end of the body 


1 de hoe grootheijt of de lengte van veele haar lighamen MS. . . . of 
wel de lengte van veele haar ’er lighamen Dutch printed version. 

2 alwaar hier te lande MS. waar mede hier te lande printed version. 
* Obviously bacilli of some sort, but otherwise unidentifiable. 



in front, and anon with the other.t’ These animalcules, 
as they appeared to me, I have shown in Fig. A. [See 
Text-fig. 4.] 

And I saw, too, sundry animalcules”’ that had very 
near the same length, and also some a bit longer. These 
moved their bodies in great bends, in comparison of the 
first animalcules, and made with their bendings so swift 
a motion, in swimming first forwards and then backwards, 
and particularly with rolling round on their long axis, 
that I couldn’t but behold them again with great wonder 

i as 3 B 

ee ig 

\ ~— 

=a — 
Sis Cc fy. 
———" Se 
a a 

[Text-Fia. 4] 

and delight: the more so because I hadn't been able to 
find them for several years, as I’ve already said. For I 
saw not alone the nimble motion of their own body; but 
the little animalcules too, which swam in great plenty 
round about these animalcules, were shoved off or driven 
away from them, just as if you imagined you saw a 
butterfly or moth flitting among a swarm of gnats, so 
that the gnats were all wafted away by the butterfly’s 
wings. ‘These animalcules I have represented in Fig. B. 

1 This very acute observation was made on other bacteria, of course, at 
a much earlier date—as already noted. It furnishes conclusive proof that 
the organisms observed were bacteria. 

2 From the following account these were evidently spirochaetes again: 
but the figures are very poor, and could hardly be identified without L.’s 
description of the organisms themselves. 


Furthermore, I saw animalcules* that were of very 
near the same thickness, but of singular length. These 
had so little” motion that I had most times to confess 
they might not be living creatures at all; yet when I 
could keep my eye on them, without getting tired, I 
could make out that they bent their body very slow, just 
bending it into a very faint curve, so that they didn’t 
move forward, or very little. ‘These animalcules, as they 
looked to me, are shown in Fig. C. 

Now I also saw yet other animalcules,* that were of 
very nigh the same thickness, but which in length even 
surpassed those last described. But you seldom saw two 
of this sort alongside, or floating off in the wet stuff, that 
were of one and the same length. ‘These animalcules * too 
were ’ in great numbers, whereof some were straight, while 
others had a kink in them, as shown in Fig. D. But 
the longer these animals were, the less motion or lfe 
could I discern in them: and notwithstanding I could 
make out no life in ’em, yet I made sure they were living 
creatures, or had been such when they were in the mouth, 
and situated on the back teeth, where many are 

But we must be still more amazed when we consider 
how these animalcules can move, and shift ’emselves 
about, in stuff as thick as this is when it is lodged upon 
and betwixt the teeth; and how hard and slow it must 
be for them to get about in such stuff. But when, on 
the other hand, the said stuff is mixed up with spittle, 
and by this mixing the animalcules find themselves in a 
fluid material, many of them feel released, as it were, and 
never stop moving, so far as the eye can see. 


? Leptothria. 
seer weignig MS. soo weynig printed version. 


* Leptothrix—almost certainly. 

* Dierkens MS. omitted from printed letter. 

sijn MS. and printed version: apparently a mistake for waren. The 
Latin version has erant, and I make the same correction. 



It must be confessed that the foregoing observations add 
little to those made previously. But bacilli, spirochaetes, and 
Leptothrix are again recognizably described—if not recogniz- 
ably figured: and this letter therefore confirms, to some 
extent, the earlier one (No. 39). It also gives us a characteristic 
glimpse of the author and his methods, and for that reason— 
if for no other—deserves notice. 

Various writers have already reproduced the illustrations 
accompanying this letter, but nobody hitherto appears to have 
made any attempt to interpret them—apart from noting that 
they represent “ bacteria”. This is to be explained, I think, 
in the usual way : most people merely glance at Leeuwenhoek’s 
figures and do not take the trouble to read his words relating 
to them, so that his excellent observations have been all too 
often misunderstood or treated as mere curiosities.’ 

A few further observations on the bacteria about the teeth 
were interpolated in a letter written to the Royal Society 
five years later. In the midst of a discussion of the eggs of 
snails, the germination of wheat, and the spat of oysters, we 
find the following digression :” 

I can't forbear to tell you also,’ most noble Sirs, that 
one of the back teeth in my mouth got loose again, and 
bothered me much in eating: so I decided to press it 
hard on the side with my thumb, with the idea of making 
the roots start out of the gum, so as to get rid of the 

Tn passing, I may also add that a recent writer (Prescott, 1930) cites 
the foregoing letter (No. 75) as evidence that “ A. von Leeuwenhoek ”’ held 
the view “that microscopic organisms were produced spontaneously from 
non-living matter.” It is difficult to conceive how anybody who has ever 
read a word of L.’s writings could make such a mistake: but perhaps 
Prescott—like many another writer who quotes L.—did not consult the 
work to which he refers. This would also explain the singular fact that he 
cites the original Latin edition of the letter (1695) but gives the pagination 
of the editio novissima (1722). 

2 From Letter 110. 10 September 1697. To the Royal Society. 
MS.Roy.Soc. Printed in Brieven, Vol. III (Sevende Vervolg, 1702); Opera 
Omnia, Vol. III (Epist. Soc. Reg., 1719); and in abbreviated English in 
Phil. Trans. (1697), Vol. XIX, No. 235, p. 790. The passage here 
translated begins on p.40 of the Dutch edition, p.35 of the Latin, and 
p. 797 of the Phil. Trans. 

° ook printed version: not in MS. 

LETTER 110. 10 SEPTEMBER 1697 253 

tooth ; which I succeeded in doing, for the tooth was 
left hanging to only a small bit of flesh, and I was able 
to snip it off very easily. 

The crown of this tooth was nearly all decayed, while 
its roots consisted of two branches ; so that the very roots 
were uncommon hollow,’ and the holes in them were 
stuffed with a soft matter. 

I took this stuff out of the hollows in the roots, and 
mixed it with clean rain-water, and set it before the 
magnifying-glass so as to see if there were as many living 
creatures in it as I had aforetime discovered in such 
material: and I must confess that the whole stuff seemed 
to me to be alive. But notwithstanding the number of 
these animalcules was so extraordinarily great (though 
they were so little withal, that ’twould take a thousand 
million of some of ’em to make up the bulk of a coarse 
sand-grain, and though several thousands were a-swim- 
ming in a quantity of water that was no bigger than a 
coarse sand-grain is), yet their number appeared even 
greater than it really was: because the animalcules, with 
their strong swimming through the water, put many little 
particles which had no life in them into a like motion, 
so that many people might well have taken these particles 
for living creatures too. 

These were Leeuwenhoek’s last recorded observations on 
the bacteria of the mouth, but there is another reference to 
bacteria which he saw in a decoction of the “fur” off his own 
tongue some years later. Although these were obviously 
putrefactive organisms, and not species proper to the human 

1 The original words are 200 dat selfs de Wortels boven gemeen hol waren. 
The Latin translator apparently took this to mean that the wpper parts of 
the roots were hollowed out (as is very probable, of course), for he renders 
these words “ superior wtriusque radicis pars admodum erat excavata”’: but 
boven gemeen is a common expression with L., and always means 
“unusually” or “out of the common run of experience.” In the Phil. 
Trans. the words “boven gemeen hol” are absurdly mistranslated 
“extraordinary whole ”’ 

2 de groote van een grof zand printed letter . . . geen grof zand MS. 


mouth, I shall quote his words here—as they are not wholly 
irrelevant in the present context. In an interesting letter 
written in June, 1708, he said:? 

At the latter end of the month of April, 1708, I was 
again seized with a high fever, which stayed with me for 
four days, rising higher each night; and as my tongue 
was again coated with a thick whitish matter, I oft-times 
removed some of it, which seemed stuck very tight 
to the parts of the tongue, with a small penknife or with a 
silver tongue-scraper: and viewing it many times through 
the magnifying-glass, I could see nought else but what I 
have described * in my previous dicconenee 

On two occasions, I took some of the foresaid stuf from 
my tongue, and put it in a small clean China coffee-cup,’ 
and then poured boiling rain-water upon it, and let 
it seethe a good half hour; with the idea of separating the 
glue-like matter (wherewith the particles seemed to be 
stuck to one another) by so doing, in order that I should 
the better be able to view the parts themselves. 

Now when the stuff which I had taken off my tongue 
had lain in the water, in which it was boiled, for about 
a fortnight,’ I saw that the water was well-nigh evaporated 
away; so I poured again a little rain-water, which had 
stood some days in a clean phial in my closet,’ into the 
boiled water aforesaid. And five or six days afterwards, 

1 Brom Letter dated 29 June 1708. To the Royal Society. MS.Roy.Soc. 
Not published in Dutch or Latin editions. English translation (incomplete) 
printed in Phil. Trans. (1708), Vol. XXVI, No. 318, pp. 210-214. I 
translate from the MS. in L.’s own hand. 

2 A reference to a letter dated 18 Oct. 1707. MS.Roy.Soc. Incomplete 
English translation in Phil. Trans. (1707), Vol. XXV, No. 312, p. 2456 
[misprinted 1456]. Not published in Dutch or Latin. 

® een schoon jndiaanse Coffe Copje MS. ‘‘a clean China Coffee-dish ”’ 
Phil. Trans. 

* ontrent veertien dagen MS. “above a Fortnight”? Phil.Trans. 

> op mijn Comptoir MS. “upon my Desk near the said boil’d Water ” 
Phil. Trans. Cf. p. 114 supra. 

LETTER OF 29 JUNE 1708 255 

I brought a thin glass tube suddenly with its one open 
end over the bottom of the porcelain cup, where most of the 
particles that had come off the tongue lay all of a heap; ’ 
with the idea that when the water entered the tube, a few 
particles from the tongue would also be carried upwards 
into the tube, so that I should thus again be enabled to 
view the particles off the tongue: in doing which,’ I saw 
an inconceivable number of exceeding small animalcules, 
and these of divers sorts. But far the greatest number 
was of one and the same bigness, yet this was so little 
that they could not be discerned but by great attention, 
through a very good magnifying-glass ; and most of these 
animalcules were abiding* where the said matter from 
the tongue lay, and I took into consideration whether the 
sald creatures might not indeed be getting their food from 
the particles of the tongue. And when these animalcules 
had been in the glass tube for about two hours, I perceived 
that a great many of ’em were dead. 

1 over hoop lagen MS. In the Phil. Trans. the translator transferred 

the adverb to the glass tube, making L. say that he “ hastily turned it 
upside down [my italics] into the bottom of the China Cup.” 

2 in welk doen MS. ‘and it happen’d as I wished” Phil. Trans. 

* haar . . . waren onthoudende MS. “ rendezvous’d ” Phil. Trans.— 
a good translation, but not a word that L. would have used. 




(LETTERS 122, 125, 144, 147, 149, 150, VII, X XIX) 

Leeuwenhoek in his’ multifarious  protistological 

wanderings during the last quarter of the X VII Century. 
We have yet to consider his equally remarkable excursions 
into similar unexplored fields at a later date. 

At the turn of the century—when he was already an old 
man, nearing his 70th birthday—he was still, despite his age, 
at the height of his powers; and during the next few years— 
between 1700 and 1716—he recorded some of his most 
interesting protozoological discoveries. These observations 
were all made on free-living forms found in water. 

In a letter written at the very beginning of 1700, 
Leeuwenhoek gave the first description and picture of 
Volvoz. The letter’ begins with an account of other observa- 
tions, and describes inter alia some gnat-larvae which he had 
found in ditch-water.? It then proceeds : 

Ie the three preceding chapters we have followed 

IT had got the foresaid water taken out of the ditches 
and runnels on the 30th of August:* and on coming 

1 Letter 122. 2 January 1700. To Sir Hans Sloane. MS.Roy.Soe. 
Published [Dutch] in Brieven, III, 152 (2nd pagination), Sevende Vervolg 
(1702): [Latin] in Opera Omnia (Epist. Soc. Reg.), III, 146 (1719) : English 
translation in Phil. Trans. (1700), Vol. XXII, No. 261, p. 509.—Curiously 
enough, Vandevelde entirely overlooks the fact that this letter contains the 
first description of Volvoz. 

2 These observations are also remarkable: for they show that L. had 
noticed the difference in posture of Anopheline and Culicine larvae in the 
water—a peculiarity now well known, but generally supposed to have been 
discovered by recent malariologists. 

* Anno 1698, as appears from the earlier part of the letter. 

LETTER 122. 2 sanuaRy 1700 257 

home, while I was busy looking at the multifarious very 
little animalcules a-swimming in this water, I saw floating 
in it, and seeming to move of themselves, a great many 
green ' round particles, of the bigness of sand-grains. 

When I brought these little bodies before the micro- 
scope, I saw that they were not simply round, but that 
their outermost membrane was everywhere beset with 
many little projecting particles,” which seemed to me to 
be triangular, with the end tapering to a point: and it 
looked to me as if, in the whole circumference of that 
little ball, eighty such particles were set, all orderly 
arranged and at equal distances from one another; so 
that upon so small a body there did stand a full two 
thousand of the said projecting particles. 

This was for me a pleasant sight, because the little 
bodies aforesaid, how oft soever I looked upon them, 
never lay still; and because too their progression was 
brought about by a rolling motion; and all the more 
because I imagined at first that they were animalcules. 
And the smaller these little bodies were, the greener in 
colour they appeared to me: whereas contrariwise, in 
the biggest (that were as big as a coarse grain of sand) 
no green colour could be made out in their * outermost 

Each of these little bodies had inclosed within it 5, 6, 7, 
nay, some even 12, very little round slobules,* in structure 
like to the body itself wherein they were contained. 

While I was keeping watch, for a good time, on one of 
the biggest round bodies, among the others, in a little 
water, I noticed that in its outermost part an opening 

' groene ronde deeltjens MS. ronde deeltjens Dutch printed version 
“reat round particles” Phil. Trans. Groene (green) is very important ; 
and “great” is an obvious mistranslation or misprint. The Latin version 
also omits “‘ green ’’—calling them simply particulae rotundae. 

2 ¢e., the individual flagellates composing the colony. 

* het MS. haar printed version. 

* i.e., the daughter-colonies. 



appeared, out of which one of the inclosed round 
globules, having a fine green colour, dropt out, and took 
on the same motion in the water as the body out of 
which it came. Afterwards, the first round body ' remained 
lying without any motion: and soon after a second 
globule, and presently a third, dropt out of it; and so 
one after another till they were all out, and each took on 
its proper motion.” 

After the lapse of several days, the first round body 
became, as it were, again mingled* with the water; for I 
could perceive no sign of it. 

What also seemed strange to me, was that I* could 
never remark, in all the motions that I had observed in 
the first round body,’ that the contained particles ° shifted 
their positions; since they never came in contact, but 
remained lying separate from one another, and orderly 
arranged withal. 

Many people, seeing these bodies a-moving in the water, 
might well swear that they were little living animals; and 
more especially when you saw them going round first one 
way, and then t’other. 

Now when a great many of the said round bodies were 
in a bottle along with many little living animals, I saw 
that after the space of three days they were all gone, 
inasmuch as I could then make out none of the said 
bodies in the bottle. 

Moreover, I had put a few drops of water (as shown 
at CD [Plate XXVI1]) in a glass tube (Fig. 1, AB) about 

1 j.e., the mother-colony. 

2 en yder een beweginge aannam. These words are in the printed version 

but not in the MS., and were probably added in the proof as an afterthought. 

* <.e., the mother-colony broke up. The word is vereenigt [=united] in 
the MS., but was changed to vermengt [=mixed ] in the printed version. 

* The word ik—which is necessary for the sense of this passage—is here 
present in the MS. but omitted in the printed version. 

° 4,e., the mother-colony. 
* «.e., the individual flagellates composing the colony. 

7b) J ad { i ‘ ; a iat 
; 4% i t : 
1 as ‘ 
1 She 
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ee i 

Hee ee i ea, RN ah ty 
Reh ve Ree: fe ae 

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facing p. 


eight inches long, and of the thickness of the quill of a 
hen’s feather." One end (A) I left open, the other end (B) 
I plugged with a bit of cork (so that betwixt D and B 
there was nothing but air), with the idea that” when I 
came to handle the tube, the water wouldn’t run out of it. 
The air being now shut up in the tube, between D and B, 
cannot remain of the same volume, or extent, but changes 
at every moment, so to speak; for one can’t approach the 
tube with the hand, the breath, or any part of the body 
that is a little warmer than the air wherein the tube is 
lying, without the air in the tube being affected by some 
part of it; and this warmth brings about an expansion 
or greater enlargement of the air (in the tube), whereby 
the water is made to move, being driven from DC towards 
A: notwithstanding we may perceive no motion in it 
with our naked eye. And just as the least warmth 
causes this outward displacement of the air in the glass 
tube, so likewise warmth readily departs from the tube, 
whereupon a movement of the water takes place* back 
from C towards B. 

In this water were included two of the foresaid round 
bodies,’ and these of the biggest sort; and contained in 
each of them were five little round particles,? which 
inclosed particles were pretty well grown in size: and in 
a third big body there lay seven round lesser particles. 
These last were uncommon small. 

After the lapse of four days, the said round bodies 
remaining shut up in the glass tube all this while, I 
perceived that in two of them the outermost membrane 

1 een schagt van een hoender [MS. honder] penne Dutch edition “of a 
Goose Quill” Phil. Trans. 

2 dat is here accidentally omitted in the MS., but restored in the printed 


aan neemt MS. is nemende printed version. 

* j.e., mother-colonies. 

° i.e., daughter-colonies. 



(which was become exceeding thin and clear) was * burst 
asunder; and that the ten particles, that were contained 
within the two big bodies, were moving about in the 
water, rolling first one way and then the other. 

Furthermore I perceived,’ after the space of five days, 
that the small particles inclosed in the third large body 
were not only grown in bigness, but I could also then 
discern that from inside these small particles other lesser 
round particles* were to come forth. After the lapse of 
five days more, this third round body was also a bit burst 
open, and its contained particles were also come out of it: 
but notwithstanding it was open on one side, it kept on 
going round in the water, and that as quick as it had 
done heretofore. 

Some days afterwards, I could make out nought but 
some little bits whereof the bigger bodies had been 
composed ; and soon after, these too went out of sight. 

Without a break I continued from day to day to watch 
these little particles that had issued from the bigger 
ones; and I always saw that they not only waxed in 
bigness, but that the particles contained within them got 
bigger too. 

At the end of September,’ I perceived that the con- 
tained particles were not so regularly round as the bigger 
bodies wherein they were inclosed, and therewithal that 
some of them were broke apieces ; and that the last particles 
that were come out of the big ones seemed not to be round, 
and lay without motion against the glass.’ 

1 waren MS.—corrected to was in printed version. 

2 dat (redundant) stands here in the MS., but has been removed in the 
printed version. 

* j.e., daughter-colonies within the daughter- colonies. This acute 
observation gave great support to the doctrine of the “ preformationists ”’ at 
a later epoch, though it was then usually accredited to Spallanzani—who 
merely repeated and confirmed L.’s observations. 

* Anno 1698. 

> The whole of the foregoing sentence is inexplicably omitted from the 
Latin version. 


Now these last bigger bodies, when they had unbur- 
dened themselves of their contained particles, or when 
they broke asunder, were quite four times less than those 
wherefrom they issued: wherefore we may conclude that 
they had not reached their full growth, or gotten their 
right food. 

We have also noted that the said round bodies agree 
in their weight with water.’ This being so, they may be 
set in motion in the water with the least movement that 
it recelveth from the air. 

I thought fit to have one such body pictured, with its 
contained particles; as shown’ in Fig. 2,at EF. In this 
body, the inclosed round particles (which had so waxed in 
bigness that they were ready to be cast out) did not lie in 
such recular order as they did in those before described ; 
and as in this one there was not so continuous a motion, 
I imagine that this was simply due to the contained 
particles not all lying at an equal distance from the centre, 
so that the round body was heaviest on the side where the 
particle furthest from the centre was placed, whence its 
motion was somewhat hindered. 

For what purpose these round bodies are created we 
know not. But as I observed that the various round 
bodies, when mixt with a great many little animals* in 
the big bottle, were all vanished in the space of three 
days, I did well ponder whether they were not created to 
serve as food for such little animals. 

Now as we see that the oft-mentioned round bodies 
come into being not of themselves,* but by generation, as 
we know all plants and seeds do (inasmuch as every seed, 

1 i¢., have the same “specific gravity’? as water. This term was 

unknown, of course, to L., though the concept was familiar; and I 
therefore render his words literally and not too “ scientifically”. 

spontaneous generation ’’. 

2 See Plate XXVI. 

L. here means mosquito-larvae, crustacea, ete., —not protozoa. 

. ee . oe 
* niet wijt haar selven—meaning “not spontaneously”, or not by 


be it never so small, is as it were endowed with its 
inclosed plant‘); so can we now be more assured than we 
ever before were heretofore * concerning the generation of 
all things. For my part, I am fully persuaded that the 
little round bodies, which are found in the bigger ones, 
serve as seeds; and that without them these big round 
bodies couldn’t be produced.° 

In the summer I divers times applied myself to the 
study of the waters lying around our town, the last 
occasion being on the 8th of October 1699: but I could 
satisfy myself no further in this matter. 

The remainder of this letter contains no other observations 
on Protozoa: and the next reference to any of these organisms 
occurs some five months later, when Leeuwenhoek very briefly 
mentions and depicts the shell of a Foraminiferan, which he 
had found in the stomach of ashrimp. He did not, of course, 
know that it was the shell of a protozoon: but as this is the 
only mention—so far as I am aware—of any Rhizopod in the 
whole of his writings, I will quote the passage. After 
discussing the anatomy of the shrimp, he describes what he 
had found in shrimps’ stomachs, and adds: 

In some of their stomachs I also discovered very little 
snail-shells, which, because of their roundness, I called 

1 Demonstrated by L. elsewhere. 
2 te vooren . . . tot nog toe—redundant in the original. 

* The foregoing description of Volvox, though perfectly intelligible in the 
original, is somewhat obscured by the circumstance that L. uses the same 
word (deeltjens=particles) throughout to denote the mother-colonies, the 
daughter-colonies, and the individual flagellates. To make his meaning 
plain I have therefore substituted “ body”’, " bigger particle ’ ’, ete., for 

‘particle”’, where it is necessary to distinguish the “ particles’’ of different 
categories. The Latin translator took a like liberty with his original, and 
rendered deeltjens by particulae rotundae, particulae majusculae, particulae 
minores, etc., aS occasion required. 

“ From Letter 125. 2 June 1700. To Frederik Adriaan, Baron van 
Rhede: [Dutch] in Brieven, Tde pete p. 196 (1702) ; atoll in Opera 
Omnia (Epist. Soc. Reg.), II, p. 186 (1719). No MS., and not in Pail. 
Trans. The Latin translation is wrongly dated January 2 (postridie Kal. 
Jan. 1700). An English version of the letter will be found in Hoole (1807), 
Vol. II, p. 266—the passage cited being on pp. 271-2. 


Enlarged from the original engravings. 

Fig. 7, ABC.—Shell of a Foraminiferan (Polystomella ?). 
Fig. 3, PQ.—The Ciliate Coleps. (The original measures only 6 mm. in length.) 

facing p. 263 


little cockles;* and these little shells were no bigger 
than a coarse sand-grain. 

In order to exhibit the pretty structure of these little 
shells before the eye, I thought ’twould not be amiss to 
set a drawing made of one of them. Fig. 7, ABC 
[Plate XX VII] shows one of these little cockles, which 
I took out of the stomach of a shrimp. 

It has been generally agreed that the shell here referred 
to was that of a Foraminiferan, but different writers have 
interpreted its species variously. For my part, I feel fairly 
confident that the picture represents a Polystomella.’ 

Leeuwenhoek’s next contribution to protozoology is 
imbedded in a _ well-known letter dealing chiefly with 
Rotifers: and the protozoological elements in this epistle 
have, it seems to me, been hitherto largely ignored or mis- 
understood. Too my mind there can be little doubt that he 
here left us an unambiguous record of his discovery of three 
different Protozoa—two Phytoflagellates (Haematococcus and 
Chlamydomonas) and a Ciliate (Coleps). But I will leave 
him to speak for himself: ° 

On the 25th of August,’ I saw that in a leaden gutter,’ 
on the front of my house, for a length of about five feet 

1 ven slakhoorntje. Hoole translates “snails”, but Sewel (1708) says 

the word denotes ‘a Cockle-shell’’; and from L.’s allusion to their 
roundness, I take this to be correct. The Latin translator called them 
limaces cochleares. 

2 Cole (1926, p. 13) takes the same view; but Miall (1912, p. 216) 
identifies the organism as Nonionina. Robert Hooke (1665, Obs. XI, p. 80; 
Scheme V, Fig. X) had previously described and figured a foraminiferan 
shell—probably Rotalia—which he had discovered in sand: but to L. his 
observation was apparently unknown. 

* Letter 144. 9 Feb. 1702. To Hendrik van Bleyswyk. Brieven (7de 
Vervolg), III, 400; Op. Omn. (Epist. Soc. Reg.), III, 380. No MS. and not 
in Phil. Trans. Partially translated into English by Hoole (1807), IJ, 
207.—Vandevelde says this letter is a “ Beschrijving van waterdiertjes, 
wellicht infusorién”’: but neither he nor anybody else appears to have 
sorted out the various “Infusoria’’ described, though Biitschli (Vol. II, 
p. 621) recognized Haematococcus. 

* Presumably anno 1701. 
> John Ray (in 1663) notes as a curiosity that in Holland “the Rain 



and a breadth of seven inches, some rain-water had 
remained standing, which had a red colour; and as it 
occurred to me that this redness might well be caused by 
red animalcules (as I had indeed seen come about in 
muddy ditches), I took a drop or so of this water and 
looked at it through the microscope; and I discovered a 
creat many animalcules* that were red, and others that 
were green, whereof the biggest looked no bigger through 
the microscope than coarse sand doth to your naked eye, 
and others smaller and smaller, each after its kind. 

These animalcules were for the most part round, and 
the green ones were somewhat yellowish in the middle of 
their bodies. 

Their bodies seemed to be composed of particles that 
presented an oval figure; and therewithal they had short 
thin instruments which stuck out a little way from the 
round contour, and wherewith they performed the motions 
of rolling round and going forward ;* and when they took a 
rest, and fixed themselves to the glass, they looked like a 
pear with a short stalk; but this stalk,’ on curious examina- 
tion, was split at the end, or divided into two, and ’twas 
with these two parts that the animalcules fixed ’emselves 
fast to the glass.” 

that falls upon the Houses is by Pipes and Gutters conveyed into a Cistern, 
and there reserved for the uses of the House, as at Venice in Italy.” It 
would appear, therefore, that gutters were not commonly installed on 
English houses at that date. (See Ray, 1673; p. 53.) 

1 The description which follows obviously refers to the Phytoflagellate 
Haematococcus pluvialis (=Sphaerella lacustris), which is very commonly 
found in gutters. This is the first account of this organism. The smaller 
green ones were probably, for the most part, Chlamydomonas—equally 
common in this situation: vide infra. 

2 waar medeze een omwentelende beweginge en voortgang te weeg bragten: 
“by means of which they caused a kind of circular motion and current in 
the water’—Hoole. This mistranslation entirely spoils the sense of this 
important passage describing the action of the flagella. 

® Hoole here interpolates “or rather this tail’—which is not in the 
original, and shows that he did not understand what L. was talking about. 

* This is a remarkably good observation of the locomotory organs of 
Haematococcus, which possesses two anterior flagella that often adhere to 
one another for a variable length at their proximal ends. 

LETTER 144. 9 FEBRUARY 1702 265 

The smallest animalcules of this sort I judged to have 
been begotten of the bigger ones. 

I did also see yet another kind of animalcules, that 
were much smaller.’ These were very clear in the body ; 
but I judged that there must have been quite a hundred 
of the former sort to every one of the latter. 

On the 31st of August, the water was so far dried up 
(owing to the great heat, which had continued for three 
days running), that if I pressed my finger on the dirt” 
lying on the lead, little more than a drop of water as big 
as a sandgrain stuck to it: and though I could discern a 
few living animalcules, which were transparent, in this 
water, yet all the green and red ones were dead. 

On the Ist of September, the stuff in the leaden gutter 
was become so thick, that it was like stiff wet clay; and 
notwithstanding all my efforts, I could discover no living 
creatures in it of the sort that I had seen before. 

At this point Leeuwenhoek leaves Haematococcus and goes 
on to describe the Rotifers which he also discovered in his 
leaden gutter; but in the course of his description he 
accurately notes that: 

The stuff in the guts of these little animals ° was most 
always red, proceeding (as I imagined) from the red 
animalcules* which they use as food: but I also saw 
afterwards a few of these little animals which hadn’t 
any of the red stuff inside them, particularly the young 
ones which had not long left their mother’s body. 

Here follow further observations on Rotifers—including 
the famous experiment in which Leeuwenhoek found that 

1 Possibly bacteria, but obviously unidentifiable from this slight 

2 A little later (4 Nov. 1704) L. says—in the words of a contemporary 
English translator (MS.Roy.Soc.)—* I don’t suffer such foul stuf to lye long 
in my gutter, but twice a year cause the lead to be scowered so clean that 
it looks just like new’”’. 

* t.e., Rotifers. 

2.€., Haematococcus. 

they can “‘return to life” after desiccation. Whilst relating 
his experiences, however, he mentions an organism which is 
almost certainly identifiable—from the figure which he 
fortunately gives—as the ciliate Coleps. He says:? 

Now divers little animalcules came before the draughts- 
man’s eye, whose structure was very like what is shown 
in [Plate XX VII] Fig. 3,’ between P and Q, whose belly 
was flat, and from which little instruments stuck out, 
wherewith it effected its progress. And as this animal- 
cule had little round globules in its body, so there were 
yet many other little animals * a-swimming in the water, 
whose whole body seemed no bigger, under the micro- 
scope, than one of these globules in the bigger sort just 
spoken of.* 

I have divers times so placed the said animalcules’ out 
of water, that they were encompassed by an amount of 
water not so big as a sand-grain; in order to see whether 
these little creatures, when all the water round them was 
evaporated away, and they were lying in nothing but air, 
would burst asunder, as I had made certain of in other 
animalcules:° and I saw that whenas the water was 

1 Brieven, III, p. 407: Op. Oman. III, p. 387. 

* In the figure as copied by Hoole (II, Pl. XVI, fig. 35) the resemblance 
to Coleps is largely lost. The original—though very small—shows quite 
clearly the characteristic barrel-like form (with one side somewhat flattened) 
of this organism. The expanded anterior end (bearing the terminal mouth), 
the caudal spines, and even the four girdles of armour-plates, are all clearly 
indicated. Biitschli noted the resemblance to Coleps, but considered the 
identification as doubtful. To me it appears certain. 

* Possibly bacteria—or perhaps flagellates. 

“ These two sentences are very clumsily constructed in the original— 
though their meaning is clear enough—and I have not attempted to improve 

* de verhaalde dierkens. It is not absolutely certain that this expression 
means the organisms just mentioned : it possibly refers to the Rotifers. If 
it really refers to the Protozoa, then the ensuing words confirm the view 
that L. was here describing Coleps; for this ciliate has a cuirass composed 
of numerous interlocking platelets, which prevent its bursting when dried. 

° Cf. Letter 18, p. 120 supra. 


almost exhaled, and the animalcule could no longer turn 
and twist itself about in it, it took on an oval figure, and 
stayed lying thus, without my being able to see that the 
moisture evaporated away out of the creature’s body, for 
it kept its oval figure. 

At this point Leeuwenhoek returns to his experiments with 
the Rotifers: but in the account of their revivification after 
drying he notes that he 

also saw two several sorts of little animalcules 
a-swimming through the water, whereof the least were so 
little, that many thousands together would not equal a 
coarse grain of sand in bigness.’ 

After some further remarks on Rotifers he then says: 

Once more we see here the unconceivable Providence, 
perfection, and order, bestowed by the Lord Creator of 
the Universe upon such little creatures which escape our 
bare eye, in order that their kind shouldn’t die out. 

From these discoveries we can well understand that in 
all falling rain, carried from gutters into water-butts, 
animalcules are to be found; and that in all kinds of 
water, standing in the open air, animalcules can turn up. 
For these animalcules can be carried over by the wind, 
along with the bits of dust floating in the air: and on the 
other hand, animalcules which are a hundred million 
times and more smaller than a coarse grain of sand, can 
be borne aloft, along with the water particles, albeit not 
as high as the clouds, but at least a little way up; and 
then when the sun goes down, they fall to earth in what 
we call dew; and they may well be taken up too and 
carried along by the wind. This is the more probable, 
since we know that in a storm the sea is so lashed on the 
shore by the wind, that drops of sea-water are found on 
trees, running down their trunks, and still salty, more 

than half-an-hour’s journey from the coast. This salt 

" Lit. cit., Brieven III, p. 409. These were evidently not Rotifers but 
Protozoa or Bacteria. 


water is judged by the vulgar (though mistakenly) to be 
the salt evaporated by heat from the sea.’ 

On the said* 4th of September, it rained a little while 
at eventide; yet so much fell, that in the leaden gutter 
aforesaid there was some water on the 5th and 6th of 
September: and this water I examined on both days, 
and discovered, in every drop that I took from the gutter, 
eight or ten of the animalcules described, though I could 
not discern a single one of the round green or red creatures 
that was alive. 

On the 6th of September, I put up seven glass tubes, in 
which I placed some of the dry stuff aforesaid out of the 
leaden gutter; pouring into some of them boiled, and 
into others unboiled rain-water.2... On the 7th of 
September I viewed the said glass tubes, and beheld with 
wonder in one of them an inconceivably great number of 
little green animalcules,* all alive, all of which seemed 
round, as before described, and a-moving among one 
another ; nay, I saw so many that the very water seemed 
to the naked eye to have a faint green colour: but how 
curiously soever I examined the other glass tubes, I could 
find no living green animalcules in them... .° 

On the 9th of September it rained a little; and two or 
three days later it rained so much, that on the 14th of 
September there was water to the depth of about a finger’s 
breadth in the leaden gutter. Of this water I took 
about two drops; and examining it, I saw a great many 
of the little round animalcules previously made mention 

* dat door de warme wytwaseminge van de Zee werd voortgebragt. These 
words were omitted by Hoole—also most of what follows. 

2 Mentioned earlier, in connexion with Rotifers, in a paragraph not here 
translated. Apparently anno 1701. 

* I here omit two lines referring to Rotifers. 

* There can hardly be any doubt that these organisms were Chlamy- 
domonas. In similar experiments I have always obtained this flagellate in 

° Further observations on Rotifers are here omitted. 


of, whereof most had the outermost part of their bodies a 
pale green, and the middle of the body quite red.’ 

On the 15th and 29th of September, on the 13th and 
27th of October, on the 25th of November, and the 9th of 
December, I continued my observations aforementioned ; 
steeping the said stuff* both in new-fallen rain, that was 
collected in an East-Indian porcelain dish, and in boiled 
and ordinary rain-water: whereof I kept notes. But as 
the upshot was always one and the same, I discarded 
these notes: and I will only say that, on the day last 
mentioned, I put some boiled water, when it had got 
nearly cold, with a little of the oft aforementioned 
dirty stuff, into a glass tube that was sealed off at one 
end, and stopt with a cork at the other, and carried it 
about in my pocket: and I found some hours afterwards 
that not only the big animalcules* . . . were swimming 
in the water, but also many others so small, that they 
looked through the microscope no bigger than a dot, such 
as you might make with a pen. And when I had carried 
this glass tube in my pocket for eight days, these last- 
mentioned animalcules were so increased that there were 
some thousands of them, both fixt on the glass and 
a-swimming in the little quantity of water. 

On the 8th of February,’ when the oft-mentioned stuff 
had lain for a few days more than five months upon 
a clean white paper in my closet, I put a little of it intoa 
clean glass tube, and poured boiled rain-water, after it 
had cooled, upon it: and after the space of about halt 
an hour, I already found one animalcule swimming about 
in the water, and many others that remained still rounded 
up; and three hours later I saw various others of this 
kind, and some small ones of a different make.” 

_ ee ee ee) ee ee ee 
1 Undoubtedly Haematococcus. 
? i.e., the dry deposit in the gutter. 
® There is a reference here to the figures, which shows that these big 
forms were Rotifers. 
* Presumably 1702. 
® Possibly Protozoa.—These observations were referred to again by L. in 



Now since we see that these animalcules can lie bedded 
so long in dry matter, as before described, and then on 
coming into water can swell out their bodies, and swim 
off; we may therefore conclude that in all pools and 
marshes, which have water standing in them in winter, 
but which dry up in summer, many kinds of animalcules 
ought to be found; and even though there were none at 
first in such waters, they would be brought thither by 
water-fowl, by way of the mud or water sticking to their 
feet and feathers.’ 

Seeing these wondrous dispensations of NATURE, 
whereby these little creatures are created so that they 
may live and continue their kind, our thoughts must be 
all abashed; and we ask ourselves, Can there even now 
be people who still hang on to the antient belief that 
living creatures are generated out of corruption ? 

About a couple of months after the foregoing lines were 
written, Leeuwenhoek sent the Royal Society some further 
observations on the animalcules occurring in rain-water. 
The following is a translation of the greater part of this 
letter : ° 

his Letter XXIX (5 Noy. 1716, to Boerhaave); Send-brieven, p. 288 (published 
1718). Vide p. 297 infra. 

1 These remarks recall a well-known passage in The Origin of Species, 
where Darwin discusses the dispersal of organisms by similar means. 

2MS. 28 April 1702. To the Royal Society. Not published in Dutch 
or Latin works. English version (abbreviated) printed in Phil. Trans. (1702), 
Vol. XXIII, No. 279, pp. 1152-1155 [where the date is wrongly given as 
1701]. I translate from the original Dutch MS. According to my numera- 
tion this is Letter 147: but Vandevelde (1924, p. 132), who did not detect 
the error in the date as printed in the Phil. Trans., calls it “‘ Brief 2 Tr 1 
[137a]”. The MS. of the English version is extant, along with the Dutch 
original, in the Royal Society collection, and is in the hand of John 
Chamberlayne.—Chamberlayne (1666-1723) was a miscellaneous writer 
and translator—said to have been conversant with 16 languages—who was 
educated at Oxford (1685) and Leyden (1688). He became a Fellow of the 
Society in 1702, and translated—as will appear presently—several of L.’s 
other letters for publication. His best known work—Magnae Britanniae 
Notitia, which went through many editions—was a rescript of a smaller 
book by his father, Edward C. It contains an interesting account of the 
Royal Society—among many other things. 

LETTER 147. 28 aprit 1702 271 

On the 19th of September, 1701, it rained a little 
while about noon, whereupon I caught some of the 
rain-water, as pure as I was able to, in a clean East- 
Indian porcelain dish :* putting this water then in a glass 
tube, in order to see whether, in such new-fallen rain, on 
standing in my closet, any living creatures would turn up. 

I examined this water several days running, and dis- 
covered therein many little bits of dust, otherwise called 
particles, such as generally float in the air, consisting of 
very little bits of burnt wood, or charcoal, wherein I 
could make out the horizontal and ascending vessels; 
also a little bit of straw, and many blackish particles 
which I imagined to be congealed particles out of smoke 
from the coals that our smiths and brewers burn: and 
among these was a pretty structure” composed of round 
globules clotted together, just lke the little stars that 
we see in the snow in winter. But I could discover no 
living creature till the 28th of September, when I dis- 
covered some exceeding small animalcules that were 
fixed to the glass, or anon swam forwards with a quivering 
motion ; which afforded me no unpleasant spectacle. 

These animalcules were so small, that I could only 
make them out by very nice scrutiny; the tube, in which 
the water was, being so big and thick; but especially 
because the animalcules seemed to me as clear as glass: 
but it looked to me as though their bodies were twice as 
long as the width of their thickest part,’ the foremost 
and hindmost parts of their bodies running somewhat to 
a point. 

z ‘in a fine China 

in een suijvere gndiaanze porsteleijyne schootel MS. 
Bason’”’ Chamberlayne. 


een aardig maaksel MS. ‘an odd Phenomenon” Chamberlayne. 

* hare lighame twee maal soo lang waren, als deselve op haar dikste sijn 
MS. “twice as long as they were big’? Chamberlayne.—The organisms 
were probably flagellates, but are obviously unidentifiable. Their attachment 
to the glass suggests Monas vulgaris, which would also fulfil the other 
requirements of the description. 




Yet from the 10th of October till the 14th of the same 
month, I could perceive no living creature, how carefully 
soever I looked. But whereas I had till now always 
examined only the uppermost part of the water that was 
in the glass tube, on the 15th of October I inspected very 
narrowly the bottom of the glass tube (which was four 
inches long, and had a diameter of a third of an inch): 
and there I saw very many of the animalcules aforesaid, 
both fixed upon the glass and swimming forth; and 
many others sat so still upon the glass, that you might 
think they were not animalcules at all; but when one of 
’em moved, among the crowd, several others next to it 
did too. 

Not being content with these my observations, because 
I misdoubted me whether there might not well have been 
some water in this tube previously, and that from this 
source these animalcules had come, and had remained 
fixed to the glass, before I poured this rain into the glass 
tube: in order to satisfy myself hereof, I procured a glass 
tube that had lain full twenty years shut up in a dry 
chest, and whereof I was assured that neither the least 
water, nor anything but air, and what is therewithal 
contained in it, could have gotten into it. 

On the 18th of October it rained in the forenoon, after 
we had had several days of strong and stormy wind: and 
I once more caught the rain in the porcelain dish, and 
after flinging away the first two lots received in it, I 
poured the third lot of water into the glass tube. 

This last water I viewed many times ; but how curiously 
soever I looked, I could make out no living creature in it, 
though I saw particles stuck to the glass, that agreed in 
bigness and figure with the animalcules aforesaid : till the 
24th of October, when I discovered three animalcules that 
were running along and swimming forward against the 
glass, and not in a straight line, but with bendings and 
turnings as they went along: and the day after, I 
discovered like animalcules in quite ten different places, 


both running forward and swimming, and that as 
plain as if you saw, with your bare eye, those little 
animals that the common man calls Water-fleas, swim- 
ming in the water.’ 

Now there lay against the glass, within the compass of 
a coarse grain of sand, more than a hundred particles 
that were of the bigness of the foresaid animalcules, 
which particles I divers times viewed one day, to discover 
if possible whether any living creature would come out of 
them,’ or turn up thereabouts; but how carefully soever 
I looked, yet could I discern no living creature among 
these particles, nor those lying hard by: until the 
28th of October, when I saw, among the particles last 
mentioned, a good five-and-twenty animalcules swimming 
forwards, as well as running upon the glass: and I did 
then discern two sorts of animalcules,® whereof the 
smallest appeared to me first shining, and then not 
shining: and their shininess, so I imagined, was observable 
whenas they swam with their back or uppermost part of 
the body turned towards my eye. These last animalcules 
had a quite different motion, in swimming forward, from 
those a bit bigger. As regards the particles that were 
fixed to the glass, I couldn’t see any change in ’em. 

I examined the said water for several days running, 
and I saw the smallest animalcules in such great plenty, 
both coursing upon the glass and swimming, at every 
spot where I cast my eye, that ‘twas amazing: and as I 
was holding the microscope in one hand, and in the other 
the glass tube (in which the water, owing to the width of 
the tube, was set in motion),* I invariably perceived that 

1 op het water MS. “in the ordinary Brooks and Canals ’’ Chamberlayne 
—a picturesque but inaccurate rendering of the original. 


ut de selve . . . soude voortkomen MS. “whether they were 

living Creatures’’ Chamberlayne. 

* Probably protozoa, but not identifiable. 

* i.e., by the warmth of his hand, producing convection-currents. 



when the animalcules were aswimming, and got off some- 
what from the glass, they were borne forward, as if they 
were not strong enough (as you might say) to swim up- 
stream: yet they alone made, as they went ahead, certain 
windings, while the bits of dust in the water (which were 
very big in comparison with the animalcules) were swept 
forward in a straight line.’ 

I have also made sure that, when I put new-fallen rain 
in a glass tube in which there was never before any 
moisture, shortly afterwards very many little air-bubbles 
made their appearance in it, and remained sticking to the 
glass: but a little while later these air-bubbles were gone. 

T'o satisfy myself further hereof, on the 6th of November 
I took once more a new glass tube, and examined it 
through the microscope: but notwithstanding I had very 
carefully shut it up, and covered it over, I saw that there 
were yet many very little bits of dust in it. On the 
6th of November it rained again, and I caught the rain, 
as before described, and put it in the glass tube; in order 
to see whether in this one also the air-bubbles would 
make their appearance, and whether they would then 
vanish from sight. 

I examined this water divers times, even after it had 
been four hours in the tube; in which time I could 
discover not more than two or three air-bubbles, which 
were on a dried-up mite,’ out of which the air seemed to 

But whereas I had stood the former glass tube upright, 
and had put another one down somewhat aslant, I now 
placed this last glass tube lying almost flat, only so that 
the opening lay a bit higher, lest the water ran out of it, 

' This passage is paraphrased by Chamberlayne, though its import is 
correctly conveyed. It can hardly be doubted that L. was here able to 
distinguish the animate from the inanimate particles. 

2 ven wijt gedroogte mit MS. ‘‘a dry Particle” Chamberlayne. I do 
not know whether the “mite’’ should be interpreted literally or 


and that the air-bubbles might keep the position that 
they had at the top of the glass; and after the lapse of 
ten hours I saw a great many air-bubbles, that were 
mostly affixed to the said dust-particles. And forasmuch 
as we know that no dry matter or any other particles, in 
which air is included, when they get under water can 
then get the water into them unless the air be first dis- 
lodged, so the same held good also for the particles that 
were in the glass tube. 

But what is one to say of this, that some of the air- 
bubbles were quite a hundred (and others several hundred) 
times bigger than the particles on which they were 
stuck ? 

Next day, in the morning, I perceived no more than 
four very little air-bubbles, and a few hours afterwards I 
couldn’t find a single one. 

I examined this water every day till the 14th of 
November, but could discover no living creature in it; 
and the day after, I had the mischance to let my tube 
drop, so that it was smashed to bits.’ 

It is not possible to identify the organisms mentioned in 
the foregoing letter, though some of them must certainly have 
been protozoa. At the end of the year, however, Leeuwenhoek 
wrote a very important epistle in which he described and 
figured several freshwater protozoa which are easily recog- 
nizable. This letter is so important, indeed, that I must 
translate almost the whole of it. It is addressed to the Royal 
Society, and runs as follows: ’” 

1 The remainder of this letter deals with other subjects, and is therefore 

2 Letter dated 25 December 1702. To the Royal Society. MS.Roy.Soc. 
Not printed in Dutch or Latin editions. English translation in Phil. Trans. 
(1703), Vol. XXIII, No. 283, pp. 1304-1311. (The MS. of this translation 
is also extant, and is in the hand of John Chamberlayne. See p. 270, 
note 2, supra.) According to my numeration this is Letter 149. Vandevelde 
numbers it ‘‘ Brief 2 Tr 3 [147] ”.—I have made my translation from the 
original Dutch MS., but have compared it with Chamberlayne’s and note 
one or two points in which his version differs. 



I take the liberty of informing you, Gentlemen, that I 
have oft heard the common people say that duckweed’, 
which floats on the water, is generated in the ground 

I could not allow of the truth of this assertion; for 
whenever I examined duckweed, I always found that one 
of these plants is produced by another, as with trees and 
other vegetables. 

Whenever I turned my attention to duckweed, I always 
noticed that it never grows in deep water, even though 
the water be small and stagnant, and without motion, 
save such as is imparted to it by the wind’; but it is 
seen in great plenty on broad sheets of water, which are 
not deep and have little motion, but especially in narrow 
and shallow ditches. 

I have also observed that in ditches wherein there is 
very little water, the duckweed is very small, in com- 
parison with that which is found on big sheets of water, 
along the banks, where the water is shallow and has but 
little motion. 

Delfshaven, belonging to our Town, lies about two 
hours’ distant from it; and from here, through a sluice 
from the River Maas, the water that runs through our 
town is let in with the flood in summertime, and this 
water is then as clear as though we had the River Maas 
itself here. 

Now with this running water there is brought in, from 
time to time, a little duckweed ; yet so little, that ’twould 
take you half an hour to collect thirty little weeds in a | 
pot all at once. I got some of the duckweed scooped out 
of this water, in an earthen pot, with lots of water, so 
that their roots might not be hurt. 

I took several of these little weeds out of the pot of water 

' het kroost MS. (alibi Eende kroost)=“ Lens palustris” of the old 
writers = Lemna of modern botanists. 


‘and that the Wind does it no harm’’ Chamberlayne. This is a 


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yee Favre jc Aha eee ere vt, 
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dis ty Petra an Ai Best end 


Philor: Transa t:M:9 84: 

FOUND ON DUCKWEED (25 Dec. 1702) 

Reduced from the engravings published in Phil. Trans. (1703). (In the 
original drawings, in red crayon, the figures are reversed.) Figures re- 
numbered to agree with original account. 

facing p. 277 

LETTER 149. 25 DECEMBER 1702 O77 

with a needle, one after the other, as nicely as I was able 
to, and put them in a glass tube of a finger’s breadth, 
that was filled to the top with water, and also in a 
smaller glass tube, and suffered their little roots to sink 
down gently; and then examining these roots with the 
microscope, I beheld with wonder many little animals 
of divers kinds, which escape our naked eye; whereof 
two sorts had long tails,* wherewith they were linked fast 
to the little roots of the duckweed. In structure these 
little animals were fashioned like a bell, and at the round 
opening they made such a stir, that the particles in the 
water thereabout were set in motion thereby, so that on 
but two occasions was I able to discern the little instru- 
ments* with which they brought about this motion. And 
though I must have seen quite 20 of these little animals 
on their long tails alongside one another very gently 
moving, with outstretcht bodies and straitened-out tails ; 
yet in an instant, as it were, they pulled their bodies and 
their tails together, and no sooner had they contracted 
their bodies and tails, than they began to stick their tails 
out again very leisurely, and stayed thus some time 

continuing their gentle motion: which sight I found 
mightily diverting. 

I got drawings made of some of these animalcules, as 
they appeared when fastened to the root of a bit of duck- 
weed. [See Plate XXVIII.*| 

Fig. 1, ABC shows a bit of duckweed of ordinary 
bigness, as it looked, when lying out of * ne water, to the 

ne eye of my ME elAneTE, 

1 Vorticellids. Cf. p. 118 supra. 

2 ““T could not see those instruments. ... Chamberlayne. This is 
not a correct rendering. L. says “soo dat ik maar twee maal hebbe 
geste .: .” 

* The figures on the Plate in Phil. Trans. were renumbered 6-12 (other 
illustrations having been added); but I have here altered their numbers to 
agree with L.’s original drawings and descriptions. Fig. 7 [12] depicts a 
leaf of duckweed not mentioned in the passages here translated. 

* buijten het water MS. “upon the water’? Chamberlayne. 


Fig. 2, DEFG shows this duckweed with its little roots, 
as it floated in a glass tube filled with water, whereby the 
roots are displayed. 

Fig. 38, HIKLMNOPQR shows a little piece of the 
root of a duckweed, as it appeared to the draughtsman 
through the microscope; in which rootlets you could 
discern the vessels, with their divisions, running long- 
ways along the root; and these rootlets (so I imagine), 
when’ they are of no further use, and as it were withered, 
get overgrown with very many peculiar long particles, 
mostly forming little figures that you might call “flowers”, 
as shown here for a short distance in Fig. 3, between K 
aad: A 

The animalcules aforesaid, that I have likened unto 
little bells, are shown in Fig. 3, between IST * and NVW,' 
whereof I have seen, upon some roots, even more than a 
hundred living, attached by their little tails, within a 
space such as HIKLM, Fig. 3; though upon other roots 
I discovered none. 

And I also saw fixed upon several roots one or even 
(though very seldom) two little cases,’ of various sizes, 
whereof the biggest is shown in Fig. 3, RXY. Out of 
this little case a little animal, with a small part of its 
body which looked roundish, made its appearance, as in 
Fig. 3, XZY: and thereupon there suddenly came out of 


‘“‘\vhen”’ is here omitted by Chamberlayne, who thus gives a slightly 
different turn to this passage. 

2 Diatoms and monads. 

* Carchesium polypinum—with branched (contractile) stem. Previously 
mentioned by L. in Letter 96. See p. 211 supra. 

‘ A group of 3 solitary individuals of Vortzcella sp. 

° Kokertjens MS. From the description and figures it is clear that the 
biggest organism here spoken of is not a protozoon but a tubicolous rotifer— 
almost certainly Limnias ceratophylli. It is certainly not Melicerta (from 
which L. clearly distinguished it), nor can it be Cothurnia (as Ehrenberg 
and others have stated). This ciliate is described a little later. The “little 
wheels ” were, of course, the cilia on the two lobes of the trochal disc—so 
interpreted by all early observers of Limnzas. 



its roundness two luttle wheels, which displayed a swift 
rotation, as shown in Fig. 3,a@bc. (The draughtsman, 
seeing the little wheels going round, and always running 
round in the same direction, could never have enough of 
looking at them, exclaiming’ “O that one could ever 
depict so wonderful a motion!”’) These little wheels 
were as Closely beset with teeth, or cogs, as the wheel of 
a watch might be: and when these animalcules had 
thus performed their motions for some time, they pulled 
their little wheels into their body again, and their body 
right into the little case; and soon after they brought a 
part of their body out of the case again, with the motions 
aforesaid ; and at another time they would stay a long 
while inside the case, as though shut up in it. But 
although I had, indeed, formerly discovered such little 
wheels on other animalcules” too, yet their bodies were 
different from these, and their cases were of a dark nature, 
so that you couldn’t easily make out the animalcules in 
them; and therewithal they seemed to be composed of 

And I also saw some cases that were several times 
smaller than that just mentioned, and these * were as 
clear as glass, so that you could see the little creatures 
lying within them quite distinctly. Fig. 3, Pdef, shows 
the case, with the animalcule Pdf, occupying a part of it, 
as it lay taking a rest. Fig. 3, ogh, shows the little case 

1 konde men soo een wonderbare beweginge altijd vertoonen MS. “‘O, 
that he could always see such a wonderful kind of motion’”’ Chamberlayne. 
I take it that the artist’s wish was to be able to portray (vertoonen) this 
motion—not that he might go on looking at it for ever. Regarding the 
artist himself, see p. 343 sq., onfra. 

2 Melicerta ringens. In later letters (MSS. 4 Nov. 1704, to Roy.Soc., 
and 28 June 1713) L. gives an admirable description of this rotifer, and 
describes how it builds its house. See Phil. Trans. (1705), Vol. XXIV, 
p. 1784: also Letter VII (Dutch and Latin works) and Phil. Trans. (1713), 
Voleex VIET; p:.160: 

* Bvidently not rotifers but tubicolous ciliates (Cothurnidae)—probably 
the common Cothwrnia cristallina, though the species cannot be determined 
from the description and figures. 


with the animalcule as it looked when it stuck part of its 
body (gh) out of it, at which time alone you could now 
and then just make out the two little wheels,’ because of 
their exceeding smallness, but only when its body was 
straightened out, for otherwise it lay drawn up short. 

Further, I discovered a little animal * whose body was 
at times long, at times drawn up short, and to the middle 
of whose body (where I imagined the undermost part of 
its belly was) a still lesser animalcule of the same make 
seemed to be fixed fast by its hinder end. Such alittle 
animal, because of its wonderful structure and manner of 
propagation, I have had drawn, and at least twice as big 
as it looks to the naked eye when you see it in the water 
and attached to the root of a bit of duckweed. Tig. 4, 
ABCDEFG, shows this creature, whereof A is the hind 
end that it hangs on by, while at CDE are shown its 
eight * horns (though others a bit smaller had six horns), 
as it looked when it had straightened itself out, for other- 
wise it can scarce reach to a quarter of this length; and 
its horns seemed to my eye to be made in so marvellous 
a manner, that the draughtsman’s art isn’t competent to 
portray them, though the artist did his best to draw a 
small bit of a horn, as shown at KLM in Fig. 5. 

In Fig. 4, at BH, is shown a little animal that is coming 
out of the first one; and formerly, when I saw such a 
little animal fixed to a bigger one, I imagined that it 
was only a young animalcule attached by chance to a big 
one; but by nicer attention to the matter, I saw that it 
was a reproduction: for I observed that whereas the 
second animalcule, at the time when I first recognized 
that it really was one, had only four very short little 

1 A misinterpretation of the peristomial cilia. In Cothurnia it is very 
common to find 2 individuals (the products of fission) in the same house. 

2 Hydra—the first description of this organism. 

* The draughtsman—as will be evident—inadvertently depicted nine 
tentacles instead of eight: ef. Plate XXVIII, fig. 4. 


body and its horns had increased in bigness, and four 
hours later still I saw that it had forsaken its mother. 

When I discovered the young animalcule aforesaid, I 
also perceived that, on the other side of the body of the 
first animal, there was situated ' a little round knob, which 
J did see getting bigger, from time to time, for the next 
few hours (as shown in Fig. 4, between G and I); and at 
last it appeared as a little pointed structure, which had 
so far grown in bigness in the course of thirteen or four- 
teen hours, that you could make out two little horns 
upon it. After the lapse of another four-and-twenty 
hours, this last-mentioned animalcule had four horns, 
whereof one was small, a second a bit bigger, and the 
other two much bigger; and these last the little animal 
stuck out at full length, or pulled in short. And another 
three hours later this little animal was gone off from his 
mother. * 

I tried to trace this reproduction further, and for this 
purpose took the duckweed away from the animalcule, so 
that I could follow it better; but next day that animal- 
cule not only lay dead, but its horns and a piece of its 
hind end were all gone, having rotted off, as you might 
call it. 

Another little animal, that had brought forth two young 
ones, not only had her body laden with many other 


aan de andere zijde .. . een rond knobbeltje zad MS. I take this 
last word to be a verb (zat=sat). Chamberlayne, however, evidently 
took it for a substantive (zaad = seed), and consequently translates ‘a round 
little knob of seed”. But I cannot reconcile this interpretation with the 
construction of the sentence as a whole, and at this period L. always spelt 
zaad (=seed, a frequent word with him) with aa—never “ zad”. ‘A knob 
of seed”’ is also an unintelligible expression. Dr A. Schierbeek (in. litt.) 
agrees with my interpretation. 

2 All the foregoing observations on the budding of Hydra are very 
remarkable. No animal which reproduces asexually by budding was known 
at that date; and the sensation caused by the similar observations of 
Trembley, and others, nearly half a century later, is in strange contrast 
with the apparent indifference which greeted L.’s discovery. 



animalcules’* (which are flat beneath, and roundish above, 
and which I have discovered in most other kinds of water, 
and which are hardly a thousandth of the size of the 
animals which they crawl on with their little feet, and 
cause annoyance to); but a much bigger sort of animal- 
cules ° whose bodies were roundish, so pestered one of 
these little animals, not only getting on her body, but also 
by clinging on to her horns, that in spite of all the struggles 
she made with her horns and body, she couldn’t shake it 
off; and I noticed afterwards that the little animal had 
lost one of her horns.* 

“ What seemed to me remarkable and wonderful, 
was that these little animals would oft-times let down 
their horns so far, that you would think, on seeing them 
through the microscope, that they were several fathoms 

At one time or another I let the draughtsman have a 
look at the horns as they were being stretched out, or 
anon pulled in; and with me he was forced to exclaim 
‘What wonders are these!” For as the creature pulled 
in its horns, they became perfectly round, and the closer 
they got to the head, the thicker they became, and when 
they were pulled right in, they formeda still bigger round 

I charged the draughtsman to draw, as well as he was 
able to, a small part of a horn when so stuck out, which 
is here shown in Fig. 6, NOP. On this part are shown 

' Evidently the “common polyp-louse”’, Trichodina pediculus. 

2 The “large polyp-louse”, Kerona. The ciliates ectoparasitic on Hydra 
were again studied and described at a much later date by Rosel von 
Rosenhof, Trembley, Baker, and others. This is the earliest account 

of them. 

* “in the scuffle’ is added here by Chamberlayne—a_ picturesque 

addition, but not authorized by L.’s own words. 

* T have translated the remainder of L.’s remarks on Hydra because they 
are so entertaining : they contain no further observations on protozoa. But 
Hydra, rotifers, and protozoa were all “ animalcules ” for L., and he did not 
separate them zoologically ; so his views on one sort are illustrative of his 
notions about all. 


the knot-like lumps, which are to be seen also in Fig. 5, 
KLM. These lumps look to me as though they were 
made up of seven round globules; to wit, one in the 
middle, which sticks up a bit above the others, and the rest 
lying round it in a rosette. 

Now if we consider what a lot of instruments must all 
be contained in a little piece like Fig. 6, in order that it 
may be not only stretched out, but also drawn in, and 
moved around, and with as many bends and knots in it too 
as you might make in a piece of string; so must we 
wonder all the more at such a contrivance. And who 
knows but what every knot-like part may not also itself 
be furnished with yet other organs, whereby they are set 
in motion. Seeing these things I was put in mind of the 
knotted threads over which people have spent so much 
time these last few years:* and I said to myself, If the 
ladies of our country could see such a wonderful and 
perfect structure, would they not have reason to bewail 
the time and gifts which they employ in making such a 
lot of useless knots, in which not the least bit of art or 
beauty is ever to be seen! 

I saw in this water, or on the duckweed, many wonderful 
animalcules, some of them getting their food from it, and 
others (as I imagined) using it as a skulking place, to 
avoid being devoured by little fishes: but the weed seemed 
only calculated to show off’ the three sorts of animalcules 

' This apparently refers to some kind of macramé-work in which L.’s 
countrywomen then indulged: but I have been unable to find any other 
reference to it in contemporary writers. 

2 maar voor genomen de drie verhaalde dierkens aan te wijsen MS. I take 

the above to be L.’s meaning. In his view, everything in nature was created 
for some purpose ; and I suppose he would have said that one of the purposes 
of duckweed is to accommodate and display animalecules such as Vorticella.— 
The last words of the above sentence were omitted by Chamberlayne— 
possibly because he could not understand what they meant. 

* L. here describes the duckweed itself, and its generation, at greater 



Whilst observing this last weed, I saw with wonder a 
creat many animalcules’ swimming in spirals through 
the water, and they were in such a great number together 
in so small a space, that they looked like a little cloud, 
visible to the naked eye, in the water; and animalcules 
of this sort I have never before seen in other waters, but 
on the second day they were nearly all gone. 

Furthermore, in this water there were so many sorts of 
animalcules that I had never discovered in any other 
waters, that I was mazed to see such a diversity of 
structures; and each too had its own proper motion, 
wherefore I many times looked upon these delightsome 
and wondrous little creatures, which quite escape the 
bare eye. 

During these observations, I saw one sort that exceeded 
many of the others in bigness, which were coupled 
together,” in which act they lay very still against the 
glass, unless a bigger sort came too near them: and as 
they lay still, you could leisurely discern those instru- 
ments wherewith they can so swiftly move themselves,° 
and even the motions of certain parts in their bodies, from 
which some would certainly conclude that they saw the 
circulation of the blood ;* but I would sooner take it for 
the chyle’ in the guts. These animalcules were so big 
that you could descry them” in a glass tube, with clear 

length. As this part of the letter—though very interesting—-is irrelevant 
to the present subject, I have omitted it, and resume the translation at the 
point where the animalcules are again referred to. 

’ Probably protozoa, but unidentifiable. 

? Probably ciliates conjugating. Cf. pp. 200, 205, 206, 213, supra. 

* Cilia, in all probability: but possibly cirrhi. 

“ This reference to the internal “circulation” is puzzling, unless L. 

actually observed the cyclosis of the food-vacuoles (in non-conjugating 
individuals) or the rhythmic pulsation of the contractile vacuoles. 

° A modern reader might perhaps consider chyle here to be a mistake 
for chyme: but in L.’s day these terms were often. used synonymously. Cf. 
Lexicon Medicum (Blankaart, 1748; p. 192)—‘‘cHYMUS, idem est quod 


® j.e., with the naked eye. 

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NG. na hae Mle ts, er 
a AW am fj aS, yep ; 4 
hae ae es : 

Oh , vi Ae 


aaa. iis 

‘ ae alee 
ue ie 
Mi i as x + hi 
ah eit Vavete tt) 

r ve ps Ahi 


Shepptels, Die ons Clete. 
wer bed. Ko~urrn = Le 
¢ ma PAL Vee oe Cho brrer en 

~ Votn. ie Se Ps ets he feos Clevta Sith-en ben 
| vegas Soro Race mit-temra Lemets_jwelolhe fer f 

praia’ Sedeg De OU SMES hs Haar beer 

Art ~m groethuys 

Oa Lemmon Cat hoa) ny tn Se feet De Cowe 
¢ eee ae cae Keot Las tae lw ge 

Sagiu, (moar Pp Oiga! eas Kaede C4. 
er, Desc Qveckiws booren Soo. Segre 
ae en Ee, I sme se 
Lens Croer Oreide grows ats f de aa hace te 
maakteL leortn_~ ats one Sop | 
Hee Kable g 4 eb Heres, epee ee | 
vt PY Se Pee, eee en ays ter hows Ale 96 4 oe : 
™welh doe. bf tol tie Sebo Arbee se ae (aw rat | 
Shkeptele is ons aS SE ny ex fy oo. long 
naa JEL oe Sotho Bin Hore 

Atl. Ze "fo-cne { dat- 4reQDe At bn Glcet | 

Hoos Shel Heerew. 


Facsimile (reduced) of original holograph MS. (25 Dec. 1702). This is a 
good sample of Leeuwenhoek’s handwriting and signature during his later 

farina m ORE 


water: and among many kinds of creatures, I saw some as 
big as sand-grains, which had as perfect a structure as our 
garden spiders.’ 

Here, Gentlemen, you have the notes that I have kept 
about my observations on duckweed and little animalcules: 
in making which I said to myself, How many creatures 
are still unbeknown to us, and how little do we yet 
understand ! 

The foregoing letter contains recognizable descriptions of 
at least five different Cillates—Vorticella, Carchesiwm, 
Cothurnia, Trichodina, and Kerona—all of which were first 
observed by Leeuwenhoek. He had, of course, described the 
Vorticellids at an earlier date, since when others had repeated 
his observations: and he had also, as we have already seen, 
previously observed the conjugation of freshwater ciliates— 
here mentioned again. But the letter is, nevertheless, full of 
protozoological novelties. 

Little more than a month later Leeuwenhoek sent the 
Royal Society another remarkable letter, which contained a 
description of the curious colonial flagellate Anthophysa 
vegetans—one of the “iron-protozoa.” This letter has been 
generally overlooked by protozoologists, and nobody hithert ° 
appears to have identified the organism described. The 
identification is, however, easy and certain. Only one inter- 
pretation of Leeuwenhoek’s description and figures is possible. 
I will now give a translation of the relevant passages in this 
highly interesting letter: ° 

' Probably water-mites. 

2 0. F. Miller, who rediscovered and named this flagellate (Volvor 
vegetans O.F.M., 1786; p. 22, Pl. III, figs. 22-25), was apparently ignorant 
of L.’s earlier observations.—I am aware that Anthophysa is mentioned 
among L.’s discoveries in the ‘ Leeuwenhoek Film” recently exhibited in 
Holland: but this mention was taken from my own note (1923), in which 
T attributed the discovery to L. without specific reference to the letter here 

* Letter dated 5 February 1703. To the Royal Society. MS.Roy.Soc. Not 
published in Dutch or Latin Works. English translation (almost complete) 
published in Phil. Trans. (1703), Vol. XXIII, No. 286, pp. 1430-1443. 
The MS. of this translation is preserved along with the Dutch original, and 
is in the hand of John Chamberlayne. The above is a new translation 
(from the MS.) of a part of the letter only.—Vandevelde (1924, p. 133) calls 
this letter “ Brief 2 Tr 4 [148] ”’; but according to my numeration it is 
Letter 150. 



At the end of the month of July, 1702, I was standing 
in front of my dwelling, beside the water’, which flowed 
with a gentle stream through our Town, and was very 
clear, and had almost the colour of the Maas water; when, 
as the sun shone bright, I saw something moving in it, 
which seemed to me a-glitter; and so I had a mind to try 
and find out what this shining matter was. 

In order to satisfy myself, I took a glass tube, having 
very near a foot’s length and a finger’s width, and after 
tying a string to it, I let it drop into the water; and when 
it was nearly half full, I pulled it out of the water and let 
it fall from a certain height straight down into the water, 
so that, being right under, the tube got filled with water.’ 

Examining this water with the magnifying-glass, I saw 
that divers sorts of animalcules were swimming about in 
it, whereof some were of a structure that I don’t remember 
to have ever before discovered in any waters. 

I viewed this water divers times one day, but couldn’t 
discover what occasioned the glittering that it had afore 
twas put in the glass tube. 

On the 4th of August, I saw, through a magnifying 
lens, that in eight or ten places there were particles 
sticking fast to the glass; so that though all the water, 
and consequently all the very small particles that were 
floating in it also, was moved (with a slight motion which 
I imparted to the tube)*, yet these particles remained 
stuck to the glass. 

This constrained me to examine them through the 
microscope, and I saw then that the particles looked like 
a complete bough off a tree, with its many twigs, as we 
might see it with the naked eye; some of them differing 
from others in the number of their twigs. 

1 j.e., the canal [in the Hippolytusbuurt |: so rendered by Chamberlayne. 

2 This passage is abbreviated by Chamberlayne. 

* This terminal bracket is not in the MS.—apparently owing to an over- 
sight: and the sentence, which is rather involved and disorderly in the 
original, I have had to rearrange somewhat in order to make its meaning 


Chamberlayne’s words are a short paraphrase. 

LETTER 150. 5 FEBRUARY 1703 287 

Nearly all of these branch-like particles were fixed by 
their little stalks to the glass, and seemed to have had 
their beginnings in a little bit of matter that was stuck 
to the glass. 

To satisfy myself further hereof, on the foresaid fourth 
of August I put some of the water that was flowing along 
in front of my dwelling into another glass tube, which 
was rather longer and wider than the first, after flinging 
away the first and second lots of water that entered the 

IT examined this water divers times; and after it had 
stood some thirty hours in the tube, I discovered the 
bough-like structures as perfect as I have before described 
them; and among others, one that lay so that the thick 
stem from which the other branches sprouted seemed 
right against my eye. 

I fixed a microscope before this last-mentioned particle, 
with the idea of finding out if ’twould grow bigger in the 
course of time. 

After the lapse of another six hours, I couldn’t discern 
that it had increased in bigness; but now I perceived 
that the extreme tips of the twigs, which were more than 
twenty! in number, were nearly all beset with round 
transparent globules,” whose diameters were quite three 
times that of the extremities of the topmost twigs. 

As I now saw that some transparent animalcules, of 
the bigness of the round globules just described, were 
moving about among the twigs, it occurred to me that 
the round globules also might be animalcules, and that 
these animalcules had made themselves fast on the 
extremities of the little twigs aforesaid.’ 

RI ROE Ea SN Oe EE De ee 

1 meer dan twintig MS. Chamberlayne wrongly translates “ about 
twenty ’’. 

? bolletjens MS. Chamberlayne translates “bubbles” —quasi belletjens. 
But I think this somewhat distorts the sense. Bol and bel are not equivalent, 
and I. does not use their diminutives indiscriminately. 

* The flagellates forming the flower-like “heads” of Anthophysa do, in 
fact, frequently break off and swim away. 



My opinion hereof was strengthened next day, when I 
saw, in the morning, after the water had been twice 
four-and-twenty hours in the tube, that nearly all the 
round globules that were on the twigs had gotten off 
them; and that some of these round globules, which I 
was sure were animalcules, were moving about among 
the branches, while a very few of them placed themselves 
again on the twigs, and stayed sitting there motionless 
for as long as I was busy looking at ’em. 

After another twelve hours’ time, I could not perceive 
that the bough-like structure was* grown any bigger; 
but I then saw that a few of the twigs were again beset 
with round globules, and that an animalcule, which was 
at least fifty times bigger than one of the globules, was 
running about on the branches: and forasmuch as the 
ends of the twigs, whereon this creature had been running, 
were once more laden with round globules, I concluded 
(though I could get no ocular proof thereof) that the big 
animalcule was dropping her young ones there.” 

On the 6th of August, I took a glass tube that was 
more than a foot long, and with a diameter of an inch; 
and this one was sealed up at one end with the flame, 
lest there might be some doubt whether the foresaid 
bough-like structure originated from the cork: and after 
I had rinsed it out once or twice, I put this glass tube in 
my closet, and viewed it many times, but I discovered no 
bough-like structures till after the water had stood in 
the glass tube for about forty hours,’ when I fastened a 
magnifying-elass to the tube, to see if the bough-lke 
structures (after I first saw them) would not grow any 
bigger. But how nicely soever I viewed them, I could 
make out no change in them. 

eee eeeeeeeeeeeeeeeeeeeeeF 


waren MS.—a false concord. The observation seems to have been 

made on one © bough”’, and I therefore translate accordingly. 
2 This was, of course, an error. The “ big animalcule” was probably a 
ciliate—some of which prey upon Anthophysa. 

° ontrent veertig wren MS. Chamberlayne mistranslates this “ above 
40 hours”’. 

at i” a ‘ ul vba 


‘im " ; eae .. : : Sas 
pay i eas id a ¥) Relea ss : ais 

a ge. teas a : a 

{ tied! a i" oan 

. ie i Roca 

’ ; : ; 
i ey en A Le > > > 

Cea Tah 
i he | ees te at 
; - 7m ie ‘24 en 

mens * a , Ri’ 
Paes” a ne an oe | 

mass \ ; rain i Ae ee en - 
cn 7. Ny w Wit bie re ne ire mi ,) Pe i 
a ir AP a : : ie My oy a eel aire! a Ay ne 

, ie ee eee 

ig Nae De iy io pear, ne ; a 
a g ce i ely eae i: By en fl pio t Py 
. 7 ii ee - Me he ee The i ih, we . Nad 
ee! 6%, Ot ce ne 
ah a Bissek er tad Pa sty ae it Ate uM " a 
; oy pe A eth Me iy ‘ol SL | hy ‘ ray i Z i 
i : vn Vy a0 0) a Teed th : ' y 
Haat eee | 
hae PI a lly ann ¥ ; 
F es ey ee ' OF a ak ? ang j , RI oy ats : 
; ®t dg : 
oe ee Wa aie i a ae | 
i De eh hw h aie aS) 0 ae 
q os ig sn ene Ms = Ne, | 
Beis Maen : We an 

4 in 


philos :Transacttl -228¢ 

LEEUWENHOER’S FIGURES OF Anthophysa vegetans 

From the engravings in Phil. Trans. (1703), illustrating his Letter of 5 Feb. 
1703. (The original drawings, in red crayon, are reversed.) Slightly 

facing p. 289 


And now I also saw that upon the extreme tips of a 
very few of the branches there were three or four, or 
sometimes even five, round globules, set beside one 
another like a rosette; which afforded no unpleasant 
spectacle. For when one such branch was fastened to 
the glass by its thick end alone (from which all the other 
lesser branches sprang), then all the twigs’ were put in 
motion by any little movement which you imparted to 
the water ; whereby also some of the aggregated globules, 
which were set thereabouts, and which you would judge 
not to be stuck fast upon the utmost twigs, were’ like- 
wise put in motion: but I assured myself, after divers 
observations, that they were really fastened thereto, 
though I could make out no structure whereby they were 
joined, owing to its exceeding thinness.” 

I let the water run very slowly out of the glass tube, in 
order that the branches (which were fastened to the glass 
by their stem, and whose twigs were kept in continual 
motion when one handled the tube) might lie against the 
glass, as the water ran off them, so that my draughtsman * 
would thus be able the better to make a pipeure of them. 
[See Plate XXX. ] 

Fig. 1, ABCDEF, shows the structure described, as it 
was lying against the glass. A represents the part that 
you would put down as the root of a plant, whereby 
alone ‘twas fastened to the glass. We see here what a 
lot of twigs there are on it, which now look rather 
disorderly ravelled together, though lying free in the 
water they were not unpleasant to behold: especially 
because their colour was like that of oaken wood, and in 
many places they were encrusted with little round 

1 alle de sprankjens MS. Chamberlayne says “all the five small 
Twigs’; but this is not in the original, and does not make sense. 

2 IT supply waren, which is missing in the original—apparently owing to 
the presence of the same word in the clause immediately preceding. 

* This sentence is much condensed in Chamberlayne’s translation. 
* Cf. p. 342 infra. 



cranules, just as if they were made up of congealed round 

At G, and hard by D, are shown the rosette-like struc- 
tures which seem to consist of several globules, and 
whereof some are also indicated at H: and though I 
couldn’t see that the structures shown at H were joined 
to twigs, yet they always moved about in the water in 
the same way as the utmost little twigs did. 

No sooner was the water poured out of the glass tube, 
than I forthwith viewed the structure aforesaid: and 
thereupon I saw swimming, between the twigs called BD 
and BE, two animalcules as small as each of the globules 
whereof the structures shown at H are made up: and 
these animalcules then went on swimming, even in the 
little water that had not yet evaporated from between 
the twigs, till my eye wearied with looking at them. 
During this observation I further saw one of the four 
globules shown at H break off, and make off as though 
swimming away, though the distance of its removal was 
not above a hair’s breadth: and this particle which swam 
off was certainly an animalcule, for it turned and twisted 
itself round about several times. And in another globule 
I did also see indeed a little motion ; but it didn’t break 
off from the others, with which it formed the figure of a 

There were, furthermore, many other little bough-lke 
structures which did not lie so orderly: and when the 
water ran off them, they took on the shapes shown in 
Fig. 2, IKL, and Fig. 3, MNO. 

What are we to say about the fabric of these little 
boughs, or tree-like growths? We can’t suppose that 
they proceed from a seminal matter in the water: but, 
with submission to better judgements, we are more 
satisfied by imagining that they are composed of some 
substance which, floating in small particles in the water, 

1 The stalk of Anthophysa is encrusted with brown particles of ferric 
hydroxide, and this is by no means a bad description of its appearance. 


is clotted together by some kind of mutual attraction. 
This won’t seem strange to us, if we bear in mind that 
whenever we file a bit of iron it gets rather hot; and if 
we apply the filed part to the filings, they’ll stay hanging 
chain-wise from it; though in nothing like the way 
such filings do with a lodestone. 

At this point Leeuwenhoek digresses into a description of 
some chemical experiments. ‘Then, after describing how he 
dissolved a little metallic silver in dilute nitric acid, he tells 
us how he witnessed the wonderful branching “ tree” which 
grew in this solution when he dropped into it “a particle of 
copper of the bigness of a sand-grain.” Such “trees” are 
now familiar to every schoolboy, but in Leeuwenhoek’s time 
they were novelties: nor has their wonder been wholly 
evaporated away by the work of modern chemists.’ It is 
clear, moreover, that Leeuwenhoek saw in the metallic “tree” 
a physical analogy—suggesting an explanation of its growth— 
to the ‘“‘tree” of Anthophysa, formed (in part) by the con- 
gealed particles of ferric hydroxide: for he adds ‘‘ I observed 
with a great deal of pleasure, how the Silver in this clear 
Water was coagulated into such bodies as are described by 
the above-mentioned Trees”’.*” Nevertheless, while recognizing 
the resemblances, he confesses that the process of growth is, 
in both cases, to him “ wholly inscrutable ”’. 

About 10 years later Leeuwenhoek sent another most 
interesting letter to the Royal Society—a letter in which he 
described anew his observations on Rotifers and Vorticellids. 
After referring to his previous observations on Melicerta, and 
its ciliary mechanism, he says :° 

1 Cf. Leduc (1911). 

® Chamberlayne’s translation.—L. gives a figure of his “ silver tree ”’ 
which is, I believe, the first ever published. His observations are, apparently, 
unknown to Leduc and other recent students of similar phenomena. 

° From Letter VII. 28 June 1713. To the Royal Society. MS.Roy.Soc. 
Published in Brieven, IV, 64 (1718); Epist. Physiol. (Op. Omn. IV), p. 63 
(1719). English translation printed in Phil. Trans. for 1713 [published 
1714], Vol. XXVIII, p.160. (The MS. of this translation—in an unknown 
hand—is preserved in the Roy. Soc. collection.) I translate directly from 
the original MS. in L.’s own hand. 


Notwithstanding I have so many times seen such 
animalcules,’ and let others see ’em too, yet one can’t be 
satisfied with just looking at* so wonderful a structure: 
chiefly because one can’t get clear on how such an 
unbelievable motion is brought about, and in the second 
place, as to what purpose this motion was for. For when 
we see any part of such a creature (that is endowed with 
motion *) moved,* we feel sure that this part wasn’t made 
for nothing, but is a necessary part of it; and conse- 
quently this wheelwork is of use to the animalcule’s body, 
though we can’t call to mind just what use it is.’ 

He then records some further observations on Rotifers— 
made “at the end of July and the beginning of August 
[1712] ’—and proceeds : 

Furthermore, I paid great attention to their revolving 
toothed wheelwork; and I saw that an incredibly great 
motion was brought about by the said instrument, in 
the water round about it, whereby many little particles, 
that could be made out with the magnifying-glass, were 
wafted towards the animalcule, while others were carried 
away from it; whereof some, being borne into the middle 
of the revolving instrument, were used as food by the 
animalcule.’ And other particles, when they got up to it, 
went off from the animalcule as quick as if it flung them 
away; seeing which, I came to the conclusion that the 
cast-off particles were no good to the creature for food. 

From this observation we may well conclude that, since 

1 Called Dierkens throughout in the Dutch printed version, but Dieryens 
in the MS. 

* te beschouwen: these words are in the printed version but not in 
the MS. 

° The words in parenthesis are in the MS. but not in the printed version. 

4 bewegen MS. dat bewogen werd printed version. 

° 4s printed version was MS. 

5 van het Dierke als tot spys gebruykt wierden Dutch printed version. 
The MS. says het Dierke als tot spijs gebruijkte (the animalcule used as 

LETTER Vil. 28 JunE 1713 293 

these animalcules can’t displace ’emselves' in the water, 
they can’t” chase after their food, like all* other creatures 
do that are endowed with motion, so that they can get 
from place to place.’ 

These animalcules,’ then, and all the others too, that 
can’t shift ’emselves from place to place, either because 
they are fixt by the tail, or otherwise, must be furnisht 
with similar instruments, in order to make a stir in 
the water; whereby they get any stuff that is in the 
water for their food and growth and for the defense° 
of their body.’ 

And when we observe the animalcules that are fixt by 
a long tail*® to something or other, like many that we have 
discovered on the little roots of duckweed,’ we see that 
they don’t merely go round in a circle with the extreme 
part of their body “ (whereby they make, in proportion to 
the littleness of their body, a big bustle in the water) ; but 
the creatures can also pull their tails together, and that 
very quick too; so that when they stick their tails out 
again, they displace the water round about them, and 

1 Underlined in MS. but not italicized in printed version. 

2 There are slight verbal differences here between the MS. and the printed 

version, but they do not affect the sense. 

alle is in Dutch printed version, but not in MS. 

* The Latin version adds “ whenever they want to” (quoties libet): but 
this is not in the Dutch. 

° Soin MS. The Dutch printed version has “ animals” (Dieren). 

S Referring to the pellets with which—as he had just described— 
Melicerta builds its house. : 

’ This passage is worded differently in the MS. and in the printed 
version, but the sense is identical. In the Phil. Trans. the two foregoing 
paragraphs were condensed into a single sentence. 

* i.e. Vorticellids. 

° Of. p. 277 sq., supra. 

” L. means that the body of the Vorticellid travels in a circle round 
the point of attachment of the stalk. The Latin translator apparently 
misunderstood these words, which he rendered “ extremitates corporis sui in 
orbem complicant’’. 


being thus come into different water,’ they can get fresh 
food out of it. 

Now I also saw a very few animalcules’ (whose bodies 
were short and thick), that were much bigger than the 
animalcules that make a little case for their dwelling- 
place,’ and these were fixed to the little roots of the 
duckweed by their hindmost or tail-like part; and not- 
withstanding they were able to move from place to place, 
they also made none the less a circular motion with the 
foremost part of their body: whence I also concluded 
that such a motion was for no other purpose than to 
make anything that would serve as food come towards 

I have ere now asked myself, What is the use of such 
a toothed wheelwork, like a cogged wheel out of a clock ? 
But if we now let our thoughts run on further, we must 
decide that such a thing is necessary, if a great stir is to 
be made in the water: for if it were a round and smooth 
wheel, it would make little motion in the water; whereas 
now every tooth that sticks out from the circumference 
causes a great stir in the water, in comparison with a 
smooth and even rotation. 

This being so, we are faced once more with the 
mysteries, and unconceivable order, which such tiny 
creatures (which quite escape one’s naked eye) are 
endowed with. 

1 Underlined in MS., but not italicized in printed versions. The phrase 
is rendered in Phil. Trans. “and so bringing fresh Water under them,’— 
which is incorrect. 

2 Clearly unidentifiable from this meagre description, but probably 

* Referring to Melicerta (and the tubicolous ciliates ?). The word here 
translated “ dwelling-place”’ is in the original hwysvesting, which may mean 
“ edification ” in any of the literal or metaphorical senses which this word 
has in English. 

“ “From whence I concluded, that those Motions serv’d some other 

purposes than only to draw their Food to ’em.” Phil. Trans. The 
translator here completely reversed the sense of L.’s words. 


Can anybody doubt, after reading the foregoing words, 
that Leeuwenhoek had, in 1718, already discovered the chief 
function of the peristomial cilia (“ wheelwork”’) of Vorticella ? 
Surely not. Old Antony knew as well as I do (and everybody 
else now does) how the Vorticellids, and many other ciliated 
organisms, capture their food from the surrounding water— 
though he misconceived the structure of the mechanism. By 
persistent study he had advanced a long way beyond his 
original interpretations of 1676,‘ and had at last reached the 

The remainder of this letter contains some further observa- 
tions on “‘animalcules”’: and as some of these—though none 
is exactly identifiable—were undoubtedly protozoa and 
bacteria, I will now quote what else he here relates : ° 

At the beginning of the month of August,’ I was in a 
garden where there was a pond well stocked with fish ; 
and pretty well all over the water there floated a thin 
scum, which looked greenish, though you couldn’t see any 
other green-stuff in the water: which seemed to me odd, 
because in other years* I had noticed that the water was 
very clear in this pond, as it was also in the ditch from 
which the pond was continually replenished; but I was 
told that when it rains, the scum goes away. 

I went a little aside, all on my own, and took a wooden 
lath, with which I touched the surface of the water ; and 
putting a little drop of the water in a green wine-glass, I 
looked at it through a microscope that I had by me: and 
I discovered in this water so unbelievably many little 
animalcules, which even through a microscope are scarce 
discernible, that no one could be made to credit it, unless 
he got a sight of it for himself; and also divers sorts of 

1 Cf. p. 118 supra. 

2 The passages which follow begin at the top of p. 68 of the Dutch 
printed works (Vol. IV, Send-brieven). 

* Presumably anno 1712: but from the final paragraph this is not 

* op andere jaren MS. “at other times”? Phil. Trans. 


large animalcules, mixt with very’ many air-bubbles, of 
extreme littleness. 

A few days’ afterwards, I asked to have a little of this 
water brought to my house, in order to examine it more 
nicely ; but I could discover nothing else in it than what 
I have just related, though I noticed a little later that 
no air-bubbles * were to be seen in it. 

Now if people rinse beer and wine glasses in such a 
pond, who can tell how many animalcules may be left in 
these glasses ? whence some of them may even get into 
our mouths. And this being so, people have no reason 
to ask me how the little animalcules, which, as I have 
said many a long year ago,’ are in the stuff between our 
teeth, and in hollow grinders,’ are able to get there. 

Thus far my notes, which I kept some years ago, and 
which I have come across within these last few days. 

Leeuwenhoek’s last recorded observations on protozoa are 
contained in a letter written in 1716 to Boerhaave.° Unfor- 
tunately they are mentioned very briefly—being sandwiched 
in between observations and speculations on spermatozoa. 
Despite their brevity, however, they are of extreme interest. 

After speaking of the spermatozoa of various animals, 
Leeuwenhoek abruptly interjects the following remarks: ‘ 

1 The word “very” (seer) is in the printed version, but not in the MS. 

* Eenige dagen MS. Eenige weynige dagen Dutch printed version. 

* Lugtbellen [underlined] in MS. The printed version has lugtbolletjes. 
* Vide p. 238 sq., supra. The “ animalcules”’ were, of course, bacteria. 

° inde stoffe . . . tussen onse tanden, ende inde holle kiesen [last 
two words underlined] MS. “in and about our Teeth” Phil. Trans. 
There are slight verbal differences here between the Dutch printed version 
and the MS., though the sense does not differ. 

®° Herman Boerhaave (1668-1738), Professor of Botany, Chemistry, 
and Medicine at Leyden— ‘a whole Medical Faculty in himself’’—is too 
famous a character to need further annotation. He was elected a Fellow of 
the Royal Society in 1730. For his life see especially Banga (1868, p. 807) 
and N. Nederl. Biogr. Woordenb. (1924), VI, 127 [a long and excellent article 
by van Leersum J. 

” From Letter XXIX. 5 November 1716. To Boerhaave. Published 
in Brieven, Vol. IV, p. 284; and (in Latin) in Opera Omnia, Vol. IV 
(Epist. Physiol.), p. 279. No MS., and not in Phil. Trans.—The passage 
here translated begins on p. 288 of the Dutch edition. 


I can’t forbear adding here, that I have allowed water- 
animalcules, mixed with a little earthy matter, to lie dry 
in my closet for a whole winter: and when I put them 
again in water, I saw some of them unfold their limbs, 
which seemed to be wrapped up inside them, and swim 
about in the water.’ I have also observed that animal- 
cules, which really belong to the waters, are to be found 
in the soil in our meadows ;” and these animalcules are 
carried thither, along with particles of water, by strong 
winds, and come not only from the canals but even from 
the sea. And notwithstanding that most of these 
creatures are unable to stand the winter’s cold, and so die, 
yet some of them survive, to propagate their kind: and 
this has been their lot from the very beginning of things. 

Then a few lines further on we strike the following gem: 

Now I must tell you that there is, right at the back 
of my house, a small flat lead, on which the rain-water 
doesn’t dry up for several days after it hath rained. In 
this water I have many a time seen, among others, some 
very little roundish animalcules, of divers sizes, and 
whereof the bodies were round, and having a diameter, 
when full grown, of about thrice the diameter of one of 
those globules that make our blood red: and in their 
bodies you could distinctly make out four round globules. 
These creatures were so vastly multiplied in a few days, 
that I was dumbfounded at it. 

I was all agog to know how this multiplication might 
come to pass: and in the end I found out that these 
animalcules lived for no longer than 30 or 36 hours, and 
that they then fixed themselves upon the glass, and 
stopped there without moving: while soon after, their 
body burst asunder, and lay divided into eight portions: 

" These were probably Rotifers, though some may possibly have been 
encysted Ciliates. 

2 This is probably a record of the first observations ever made on soil- 



and these were actually young animalcules, for in five or 
six seconds some of them swam off. 

Inasmuch as one animalcule thus begets 8 little ones, 
and each of these again brings forth 8: then there would 
be produced, in the course of 9 days, two hundred and 
sixty-two thousand one hundred and forty-four animal- 
cules from a single animalcule: 

In 30 hours; or 13 (days, 70... 8 animalcules 
cK opto eae © C7 Renee Pe 64 animalcules 
in AF dayseese 512 
in 6 <dayaeseer 4096 
in 7% days.......82768 

in 9 days....262144 animalcules. 

From the size and shape of these animalcules, as well as 
from their habitat and method of reproduction, it is obvious 
that they were some common phytoflagellate ; and it is highly 
probable, since no mention is made of their colour, that they 
were not the forms previously described (to wit, Haematococcus 
and Chlamydomonas). I have very little doubt that the 
description applies to Polytoma—of which it is, indeed, so far 
as it goes, an astonishingly good description.’ The division 
of the parent body into 4, and then into 8; the bursting of 
the enclosing membrane, and the swimming away of the 
daughter-individuals,—all this was observed and recorded 
with remarkable accuracy. 

How Leeuwenhoek was able to discover, with the limited 
means at his disposal, the facts which are here so simply set 

" Tam glad to find that Biitschli (Vol. II, p. 621) long ago arrived at the 
same conclusion. 


forth, must remain for ever a marvel. On reading these 
passages the modern protozoologist, knowing the patience 
and perseverance needed to make such observations—even 
with adequate instruments, and with the accumulated informa- 
tion of the next 200 years to help him—can only regard this 
extraordinary old man,’ as he regarded his “little animals”, 
with dumbfounded admiration. 

—Door Arbeit en Naarstigheijt 
komt men tot saaken die men 
te vooren onna speurligk agten. 
Actum desen 30: April 1698 

1 L. was 84 years of age when this letter was written—‘ in the autumn 
of his life,” as he says a little later (cf. p. 88). 



HE following supplementary notes—dealing with very 
various subjects—are collected together here simply 
because they are too long to print as footnotes to the 

foregoing text. They contain much that is important for the 
student of Leeuwenhoek and his writings, but the reader will 
please bear in mind that they are notes and explanations 
only—not full dissertations on the subjects treated. My 
information has been gathered from many sources during 
many years, but is still far from complete: and I offer it to fellow- 
students merely in the hope that it may help them in their 
own studies. On some matters I could, indeed, say much in 
addition: but as Father Antony himself would say, “I will 
spare you more, for ’twould else take all too long a-writing.”’ 


As the curious name “ Leeuwenhoek ”’ has, seemingly, at 
all times been a stumbling-block to foreigners (and has even 
puzzled Dutch scholars), the following annotations may not 
be amiss. 

LEEUWENHOEK, as a surname, appeared until quite recently 
to be extinct. I have been unable to find anybody bearing it 
since the middle of the X VIII Century: but my researches in 
this connexion were only superficial, and Mr Bouricius has 
delved deeper and has deservedly been more successful. He 
has discovered’ that there are still Leeuwenhoeks living in 
Holland—“ between Oudewater and Gouda.” ‘They are, so 
‘ Bouricius believes,’ descendants from Antony’s uncle * Huych 
[=Hugh]|—his father’s only brother. (See the Family Tree, 

’ Cf. Schierbeek (1929, 1930). 

2 Mr Bouricius’s researches—though unpublished—seem to have been 
very thorough: for Schierbeek (1930), who has seen his notes, says that 
“the genealogy is completely ascertained’’ of these present-day Leeuwenhoeks. 

* “ Oudoom”’ [ = great-uncle] according to Schierbeek (1930). 


p. 18 supra.) Nevertheless, it is certain that, at the present 
day, there can be no Leeuwenhoeks who are directly descended 
from the great Antony himself: for he was the only son of 
his father, and none of his male issue outgrewinfancy. His 
sisters married—and so changed their names—while his only 
surviving daughter remained unmarried. 

The literal meaning of the name ‘‘ Leeuwenhoek”’ is 
obvious: for leeww means a lion, and a hoek is a corner or 
angle. (Accordingly, the name was neatly graecolatinized '— 
in Antony's own lifetime—into “ Leogonus”.) That the 
name itself is probably a place-name seems equally obvious, 
especially as we find it coupled with van. A very plausible 
derivation has been found recently by Bouricius (1924, 1925). 
According to him, Antony’s forefathers resided in a corner- 
house by the Leeuwenpoort (= Liongate) in the HKast-End of 
Delft : * and consequently they were, in all probability, known 
to their neighbours as the family “from the corner of the 
Liongate ” (van [den] Leewwen[poorts] hoek). 

At the present day there is nothing in Delft to connect 
Leeuwenhoek and his family with the topography of the place. 
It is true there is his effigy on the railings round the playground 
of a girls school in the Oude Delft; but this was put there 
recently in error.’ And there is also, of course, a modern road 
called Antony van Leeuwenhoek singel—outside the old town, 
and leading to the railway station. 

For the orthography of the name ANTONY VAN 
LEEUWENHOEK there is good authority. In his early life, 
however, he signed himself “ Antonj Ieeuwenhoeck ’’—the 
christian name ending with a longz (not English 7) and the 
surname with ch, and without van. This is the spelling in all 
MS. signatures up to and including Letter 39 (17 Sept. 1683): 
but Letters 40, 41, and 42 are signed “ Antonj Leeuwenhoek ”— 

1 Cf. the panegyric poem prefixed to the first volume of the Opera 

2 In early days the town of Delft was fortified by walls and moats, 
communicating with the outside by various “ gates’? (poorten). This 
enclosure was originally effected about A.D. 1070-1072 by Duke Godfrey of 
Lorraine, the Hunchback (Govert mit den bult, or den Bultenaer). Some of 
these gates are still standing—more or less: but the Leewwenpoort was not 
one of them. It was an alley near the East Gate (Oostpoort), and has now 
vanished. Cf. Boitet (1729, p. 592), Bouricius (1924, 1925). 

* See p. 338 seq. 


still without van, but with final -/ in place of -ck. Letter 43 
(5 Jan. 1685) is the first one signed “‘ Anton} van Leeuwenhoek ”’ 
—with long i, with van, and with -/: and thereafter he appears 
generally to have written his name thus—that is, for the last 
38 years of his life. In the year 1685-6, however, he himself 
seems to have been in some perplexity regarding his signature : 
for Letters 44 (23 Jan. 1685), 46 (13 July 1685), and 48 
(22. Jan. 1686) are again signed “‘ Antonj Leeuwenhoek ”, while 
Letter 45 (30 Mar. 1685) is signed “A: v: Leeuwenhoek ” 
and Letter 47 (12 Oct. 1685) simply “‘A: Leeuwenhoek.” ’ 
Examples of his signature at different dates are shown in 
Plates V, X, and XXIX. 

In the Dutch published letters, the long 7 of the forename 
was generally printed as a short <—though sometimes as a y. 
It is therefore questionable whether “ Antoni” or “ Antony” 
is to be preferred. I adopt the latter spelling as it is conform- 
able with English usage,” and because an English y is a 
justifiable equivalent of the long 7. We have in English no 
such letter; and a terminal 7 not only appears strange to us, 
but may even lead—as I can testify from experience—to 
ludicrous mispronunciation of the name. I may add, for the 
information of English readers, that the name ‘“ Antony” is 
not accented on the first syllable in Dutch (as it is in English), 
but on the second: Antény—not Antony. 

On the memorial—in the Old Church at Delft—erected to 
Antony. by his daughter Maria, the full name is latinized as 
Antonius a Leeuwenhoek (the form in which it usually appears 
in the Latin translations * of his works). But curiously enough 
the Dutch inscription on the stone slab covering his grave gives 

' Haaxman (1875, p. 6 note) has already discussed the proper spelling of 
L.’s name, and adopted the same spelling as I do: but he had seen only a 
small percentage of the extant MSS.—having consulted none of those in the 
Roy. Soe. collection—and therefore had not the support (which I can claim) 
of some 150 autograph signatures. Had he seen these, he would probably 
have expressed his opinion more emphatically. 

* Though L.’s chief Dutch biographer—Haaxman (1871, 1875)—also 
invariably styles him ‘“ Antony,” Bouricius (1924, 1925), for reasons which 
are not evident, prefers to call him ‘“ Anthony”; while Schierbeek (1930) 
now names him “ Anthoni,’ and some other recent Dutch writers 
“* Anthonie.”’ 

* Antonius de Leeuwenhoek also occurs, and possibly accounts for some 
recent writers’ miscalling him ‘‘ de Leeuwenhoek”’ (instead of van L.). 


his name as “ Anthony van Leewenhoek’’—the w having dropped 
out of the surname, and an / and a y having crept into 
the first name. In old Dutch—as in modern English—it is 
quite usual to find “Anthony” spelled with an h. The 
objection to spelling Leeuwenhoek’s name thus is that he 
never—as far as | know—so spelled it himself.’ 

Authority might thus be found for a variety of spellings : 
and if importance were attached to the orthographical vagaries 
of Leeuwenhoek’s contemporaries, and of his interpreters and 
commentators down to the present day, any one of a long list of 
variant literal combinations might easily be advocated. I will 
merely note here that in the English versions of his epistles, 
published in the Philosophical T'ransactions, his surname is 
spelled in no less than 19 different ways. It appears as 
Leewenhoeck, Leeuwenhoeck, Leeuwenhoeek, Leewenhook, 
Lewenhoeck, Leeuwenhoek, Leuwenhook, lLeevvenhoeck, 
Leewenhoek, Leeuwenhoek, Leuwenhock, Leuwenhoeck, 
Leuvenhook, Lewenhoek, Lewuenhoek, Lewuenhoeck, 
Leewuenhoek, Leewnenhoek, and Leeuenhoek. Most of these 
spellings, however, are certainly due to misprints or mis- 
readings of his signature. 

It is further noteworthy that Leeuwenhoek’s name has 
suffered the most extraordinary mutations, mutilations, and 
perversions at the hands of foreigners. Germans, for example, 
commonly call him “Anton von Leuwenhoek ’”’—and_pro- 
nounce the name as though spelled thus in their own 
language; while to the French he is generally “ Antoine 
Leuwenhoeck ’’—if nothing worse. It is almost the rule, 
moreover, to find his name spelled in several different ways 
by the same writer—be he English, French, or German. 
Wrisbere (1765), for example, refers to Leeuwenhoek thrice— 
calling him (in Latin) ‘“ Loewenhoeckius,”’ “ Lavenochius,” 
and ‘‘ Loewenhoeck”’ on each several occasion. (Hxamples 
could easily be multiplied.) But perhaps the most remarkable 
transformations occur in Italian writings—even in those of 
his contemporaries and immediate followers. As instances I 
may cite Vallisneri, who usually called Leeuwenhoek 
“‘ Lewenoeckio ” but on at least one occasion *‘ Le Wenocchio ” ; 

" The name bestowed upon him at his baptism, however, was neither 
Antony nor Anthoni, but ‘‘Thonis.”’ (See Plate III.) 


while the illustrious and erudite Spallanzani regularly dubbed 
him ‘‘ Levenoecchio’”’. ‘To Buonanni he was just “ Lauenoch”’. 

Foreigners generally find great difficulty not only in 
spelling Leeuwenhoek’s name but also in pronouncing it. 
On the assumption, apparently, that it issome kind of tongue- 
twister in an unknown and barbarous lingo, they invent and 
emit noises unintelligible to any Hollander. Some of the 
more confident commentators, however, tell us how to pro- 
nounce the name properly. For example, Richardson (1885) 
informs us that it should be “pronounced in English fashion 
Leuvenhock”. J do not know why it should ever be pro- 
nounced English-fashion—rather than Dutch-fashion: nor 
can I imagine any reason for so singularly mispronouncing a 
plain Dutch word. Certainly no native of Holland would 
recognize ‘‘ Leuvenhock’”—pronounced English-fashion—if 
he were to hear it. But I can assure my fellow-country- 
men that the name ‘“‘ Leeuwenhoek” is pure Dutch, and 
not so difficult to pronounce as it looks; and that no 
Hollander will misunderstand if it be spoken as though 
written in English “‘ Laywenhook”. This does not—as I am 
well aware—represent modern Dutch pronunciation exactly ; 
but it is phonetically far better than the common English 
mispronunciations resembling ‘“‘ Lervenherk ” or “ Loivenherk ” 
or “ Luvenhock”. The Dutch diphthong eeu(w) is closely 
similar in sound to ay-oo (said quickly) in English: and there 
is surely no conceivable reason why the Dutch oe (exactly 
equivalent to oo in English, and to our own oe in the words 
“shoe” and “canoe”) should be pronounced as though it 
were German, French, Italian, or Latin. 

The reader will no doubt recall (see p. 43 supra) that 
Constantijn Huygens—who knew English well—said that 
Leeuwenhoek’s name would be written “according to our 
orthography ” as “ Leawenhook”. But the phonetic value of 
ea in English is not now constant: it differs widely in 
different words. Huygens evidently had in mind the modern 
sound of these vowels in words such as “ great” or “ break ”"— 
not in “real”, ‘seal’, ‘‘Chelsea”, or “bread”. (For some 
judicious comments on this subject see Wheatley’s edition of 
Pepys: preliminary “Particulars”, ad finem.) In Huygens’s 
time ea in most English words “sounded as it still does in 
‘oreat’” (Bense, 1925; p. 205). He therefore meant that 
‘““Tieeuwenhoek”’ should be pronounced as ‘‘ Laywenhook ” in 
English—as I have already said. 


The Swedish traveller Bjérnstahl, who visited Leeuwen- 
hoek’s tomb in 1774, says that the name should be pronounced 
“ Tewenhuk” (more germanico). Jam not prepared to dispute 
this: it is perhaps as near the truth as my own foregoing 
attempt to imitate the sound in English. But when the same 
writer adds! that the name ‘‘ Leeuwenhoek” means “ einen 
Greif” [i.e., a griffin], I must part company with him. This 
strange interpretation appears, indeed, to rest upon nothing 
but an erroneous inference from the mutilated heraldic device 
on the tombstone covering Antony and his daughter Maria— 
which still shows a flying eagle bearing a scutcheon, on which 
the Leeuwenhoek coat-of-arms was formerly emblazoned.” 

It will be evident, therefore, that there is now no real 
mystery enshrouding the name “ Leeuwenhoek”. We know 
well enough how to spell it, how to speak it, what it means, 
and where it came from. Any doubts which may still exist 
about it are, apparently, due to mistakes or misunderstandings 
manufactured by credulous or incompetent commentators. 
No profound research is needed to arrive at such a conclusion : 
it must be obvious to everybody—no matter what his nation- 
ality—who devotes more than passing attention to the matter. 


Leeuwenhoek’s only language was Dutch—not the modern 
literary language of the Netherlands, nor Old Dutch (properly 
so called), but the ‘‘ Nether-Dutch ” commonly spoken in the 
Province of South Holland in the XVIJ Century. It is a 
language far removed from that of “Reynard the Fox” 
(Vanden Vos Reinaerde, written circa A.D. 1250), and is not 
even so archaic as the Dutch Bible (which dates from 1637, 
though—like the English—it contains much earlier elements). 
Consequently, for any educated Hollander of the present day 
it is no harder to understand than colloquial English of the 
same period is nowadays to an educated Englishman. 

IT have heard it said that Leeuwenhoek’s language is 
more like Cape Dutch—the “ Taal” or “ Afrikaans” now 

1 Vide Bjornstahl (1780-84) ; Vol. V, p. 364 of German translation (1782). 

? The coat-of-arms proper (now gone) consisted of a don rampant azure, 
tongued and clawed gules, in a field or. See Haaxman (1875), p. 125, and 
Morre (1912), p. 15.—The grave was despoiled during the French occupation 
of Delft. 



spoken in South Africa—than modern Dutch: and I have 
been credibly informed that a certain well-known historian 
of zoology actually engaged a Boer from Cape Colony (in 
preference to an educated Hollander) to translate some of 
Leeuwenhoek’s original letters for him, in the belief that he 
would thus obtain the most accurate English rendering. (I 
have also been told that the Cape Dutchman declined the task 
after inspecting the early MSS. He is said to have expressed 
the opinion that they were really not written in Dutch at all !) 
So far as I can judge, Leeuwenhoek’s speech was very different 
from modern Afrikaans: but I have no accurate knowledge of 
this language—what little I know being derived chiefly from 
perusal of the interesting work of Bosman (1928). In any case 
it is certainly a mistake to suppose—as I know some people 
do—that Leeuwenhoek’s Dutch is as different from modern 
Dutch as Chaucer’s English is from modern English. Any- 
body who can read modern Dutch can, with a little patience 
and practice, easily read Leeuwenhoek's printed letters. 

That Leeuwenhoek knew no language but his own is 
attested by himself and others. For example, he refers in 
Letter 2 (ante, p. 42) to his lack of education in this 
respect and Molyneux also comments upon it (ante, p. 58). 
Numerous passages in the published Letters might easily be 
cited to the same purpose,’ but perhaps the best testimony is 
furnished by an unpublished letter written to Oldenburg in 
1676. Oldenburg, it appears, had written to suggest that 
Leeuwenhoek should conduct his future correspondence either 
in French (which he supposed Leeuwenhoek must know) or in 
English (for which he imagined a translator could readily be 
found in Delft, as so many English were then in Holland). 
Leeuwenhoek answered as follows :” 

" Letter 15 (21 April 1676, to Oldenburg: MS.Roy.Soc.), of which an 
incomplete translation was published in the Phil. Trans. (Vol. XI, No. 127, 
p. 653. 1676.), is sometimes quoted in evidence. In this letter L. is made 
to say: © I, by reason of my unskilfulness in the English Tongue, could have 
little more than the contentment of viewing the elegant Cuts’’ [in Grew’s 
Anatomy of Trunks]. But unfortunately the words here italicized (by me) 
are not in the original MS. They are a gloss by the translator (Oldenburg), 
and not L.’s own words. Nevertheless, the passage testifies that Oldenburg 
was aware that L. did not know English. 

* From Letter 13a. 22 January 1676. To Oldenburg. Unpublished. 
MS.Roy.Soec. (The original is in Dutch—the above being my translation.) 


Your favour of the 28th December [1675] has reached 
me safely, from which I see that you doubt not but I have 
a sufficient knowledge of the French language ; but I must 
confess, to my sorrow, that I don’t know any tongue but 
the Nether-Dutch, to which I was brought up: but if 
you write to me in French or Latin, I can manage it 
all right, as I have friends enough here who can translate 
itforme. But with English I can’t cope, since the death 
of a certain Gentleman who was well versed in that tongue. 
I grant you there be plenty of the English nation knock- 
ing about everywhere, but not all of them are competent 
to translate the T'’ransactions out of English into Dutch: 
for when I inquired here for a fit person, I was directed to 
the chanter of the English Church (who offers his services 
also for teaching English). This fellow, presuming to do 
what I wanted, and having translated for me a bit 
that roused my curiosity, twas so lame I could make 
neither head nor tail of it. 

In a slightly earlier letter” he also remarks parenthetically 
(since I don’t understand English, to my sorrow, 
and there's nobody in this town who has the ability to translate 
into Dutch for me)”. It may be taken as certain, therefore, 
that Leeuwenhoek could neither speak nor read any language 
but his own. Consequently—and this must always be remem- 
bered—he was never able to detect or correct mistakes 
committed by the translators of his letters into English and 
Latin. As these translators were often wholly ignorant of the 
things which Leeuwenhoek was attempting to describe, their 
versions should always be read with caution. In all cases 
of doubt it is necessary to refer—whenever possible—to his 
own original words. 
One of Leeuwenhoek’s present-day countrymen,’ looking 


1 Howell, at an earlier date (1622), says “ There is no part of Europe so 
hanted with all sorts of Foreigners as the Netherlands”’ (ed. 1705, p. 87). 

2 Letter 13. To Oldenburg. 20 December 1675. MS.Roy.Soc. 

* Becking (1924). 


down upon him from the heights of his own wisdom, regards him 
as a greatly over-rated dilettante '—“ illiterate,” “ uncultured,” 
‘‘common to a degree ’’—and even goes so far as to aver that 
this “bourgeois satisfait . . . rather took a pride in the 
fact that he knew neither French, Latin, English nor German.” 
But I know of no evidence in support of such a statement, 
and it is clearly contradicted by the words “to my sorrow ”’ 
(tot mijn leetwesen) in the two foregoing extracts. 
Leeuwenhoek was always ready to confess his ignorance, but 
he was never proud of it. He would undoubtedly have said 
that nobody but a fool could pride himself on knowing less 
than other people. 

Although—as already remarked—Leeuwenhoek’s language 
presents few difficulties to his own countrymen, it must be 
confessed that to foreigners his words often appear at first 
sight very queer, and occasionally even enigmatic. But this 
is merely due to certain peculiarities of spelling and speech to 
which one soon becomes accustomed—peculiarities proper to 
his age and country, and not eccentricities or comicalities 
proper to himself. We see exactly comparable features in 
English of the same period, and inexperienced modern readers 
apparently tend to regard both as humorous. For example, I 
have seen people laugh at a grave sentence in Robert Hooke 
because the word “ guess” is spelled “ Ghesse”’: while Saville 
Kent refers to the ‘‘quaint style of diction” of Oldenburg’s 
excellent contemporary English translation of Leeuwenhoek’s 
Letter 18 merely, I believe, because it was not couched in the 
current English of 1880. Every serious student of Leeuwen- 
hoek and Hooke must realize at once, however, that there is 
nothing either “quaint” or “funny” about their phraseology 
or spellings—any more than there is about Tyndale’s English 
translation of the Gospel, or Spinoza’s Dutch writings on 

The following few notes are not intended for Leeuwenhoek’s 
learned fellow-countrymen or for professional philologists, 
but for poor foreign scholars like myself—“‘illiterate”” and 
“‘c¢ommon’—who have no special knowledge of the peculiarities 
of his language, but who want to read and understand what 
he himself wrote. I design merely to give a few hints such 

1 “ dilettant”’ in Becking’s own Italian-Dutch-American-English. 


as I should myself have found helpful when I first began to 
try and read his own writings. 

Leeuwenhoek’s speech is (pace Professor Dr Becking) an 
interesting example of the Dutch of the transitional period 
between the language of the Bible and the modern tongue. 
It preserves not a few genuine old words, and sometimes 
reflects the troubled history of his time; for we find, inter- 
spersed among his homely native vocabulary, numerous foreign 
intruders—mostly of French origin—which have not taken 
root in the language, and which will therefore be sought in 
vain in a modern Dutch-English dictionary. (I may instance 
the following, which all occur frequently in Leeuwenhoek’s 
early letters: presentatie, swperfitie, circumferentie, [en |devotr, 
observeeren, imploieren, imagineeren, continuelyk.) The inter- 
pretation of such words is, fortunately, seldom difficult for an 
English reader, because we have incorporated their counter- 
parts into our own tongue. 

There is a vast difference between the early letters and the 
last letters—not only in the handwriting but also in the words 
and wording.' ‘he first letters are comparatively archaic, 
and inscribed in the Dutch character: the last are far more 
“modern ’’, and written in the “Italian”? hand which is now 
universal. Between these extremes, however, all intermediates 
occur. I would also note that the spellings and punctuation 
are more “modern” and uniform in the Dutch printed letters 
than they are in the original manuscripts. But this is also 
true of English writings of the same period—so far as I have 
studied them. “Correct” and uniform spelling seems to be 
generally due to printers and compositors, rather than to 
scholars and authors, in all printed languages. 

Only the archaic and the irregular spellings likely to 
trouble present-day foreign readers of Leeuwenhoek’s early 
letters will be noted here. The genuine archaisms—as distinct 
from the variations in spelling characteristic of the erratic 
orthography of the period—are chiefly the following : 

1 T am not concerned here with L.’s style of writing, which I can judge 
only as a foreigner. His own countrymen not seldom speak of it con- 
temptuously—Becking, for instance, and earlier Pijzel (1875), who describes 
it as “ pretty slovenly” (vrij slordig). 



(1) VowELs 

ae is written for aa (e.g. aen, daer, waer, aengaen, for 
aan, daar, waar, aangaan).’ 

eij may represent ez: as weijnig [ weinig |, Mez | Mei], etc. 

7, y, and 7 are often interchangeable, and do not always 
correspond with the modern usage of 7, 7, and y. 
The diphthong uy often stands for modern we. 
Spellings such as the following are thus common: 
jk, jmagineer, duijsent, huijs, Antonj [= ik, imagineer, 
duizend, huis, Antony]. 

ou is occasionally written for oe: e.g. genouch | genoeg |. 

we often occurs instead of ew or ww: e.g. curiues,” 
generues, figuer [= curieus, genereus, figuur]. 

ue may represent wu: e.g. vuier, muyer, [= vuur, 
muur |. 


c or ck commonly stands for /& (or sometimes £h), 
Leeuwenhoek regularly wrote ick [for ik], welcke 
[welke], oock [ook], malcander [malkander], clootgens 
[klootjes|, comen [komen], druckingh |drukking], 
trecking | trekking |, ete. 

ch for g. For example nochtans [nogtans], wedjnich 
[weinig]. The terminal was subject to elision, 
however, before a following aspirate: thus L. wrote 
hollicheijt [holligheid = holheid]. 

cx or cka for ks. Examples: sulca, sulckax [zulks]. 

d = dt = t. Examples: hadt [had], edethetjdt 
[edelheid], Engelant [Engeland], Hollant | Holland], 
goet [goed], hucjt [huid], zad [zat]. 

f = ff = v. Examples: halff [half], self [zelf], off 
[of |, beneffens [benevens |. 

— 7. Examples: diertgens [diertjes], deeltgen 
[deeltje] . 

gh=g. .g.langh [lang], hoogh [hoog], verwonderingh 

[verwondering ]. 

‘ It may be noted, however, that L. generally spelled the noun haar 

[= Engl. hair] as haiy—not haer. He adopted the latter spelling for the 
possessive pronoun haar [ = Engl. her, their ]. 

2 L. also wrote curieuws and cwrius. .He also wrote coulewr or couluer 

[for klewr] indifferently. © 


qu=kw=k. Hig. quaet [kwaad], quaelijck [kwalijk], 
manqueeren | mankeeren |. 

s = z. Hxamples of this equivalency are too numerous 
for selection. Words such as sin [zijn], dese [deze], 
seer [zeer] occur copiously on every page of the 
early manuscripts. 

sch and ssch sometimes stand for s or ss. Examples: 
wasch | Du. was = Engl. wax], volwassche [| volwassen].' 
We even find sch = z occasionally-—as in schonne- 
schijn | zonneschijn]. 

th is occasionally written for ¢. E.g. voortseth 
[ voortzet ]. 

x sometimes represents modern fs. Hxample: exter 
[ekster ]. 

The wrregular and capricious spellings—common in English 
and Dutch of Leeuwenhoek’s period, and of no philological 
importance—are too numerous to mention. Variants may 
often be found in the very same sentence. Itis perhaps worth 
noting, however, that certain spellings are phonetically 
interesting—the omission of letters indicating, for example, 
that they were commonly not pronounced at that date. Thus, 
the final -n (now silent in Dutch, though still heard in 
Flemish) in a word like volwassen was sometimes unwritten 
(volwassche) : while Leeuwenhoek also sometimes wrote seder 
(for sedert), ondecking (for ontdekking), schilpad (for schildpad), 
ert (for erwt) etc. He also occasionally added a consonant 
where it is properly lacking—as in pampvter (for papier) and 
miscroscope (for microscoop). The former is a vulgarism, the 
latter a mistake. What appears at first sight to be a mis- 
spelling is occasionally, however, an earlier form—such as the 
word mergen (A.-S. Mergen), which Leeuwenhoek regularly 
wrote for morgen (= Engl. morning, morrow) in his early 
letters. Omme (for om: O.Du. ombe) occurs very frequently ; 
while omtrent and ontrent are one as common as the other. 

The only other obsolete usages likely to trouble modern 
foreign readers are the frequent insertion of the negative 
adverb en in phrases such as “ alsoo ick niet en versta ”, “ ick 
miet en can”, “dat ick daer gansch geen sin utjt en conde 

' _s and -ce may also represent -sch(e): thus, in Letter 13a we find “ de 

france tael”’ and “ het frans”’ in the same sentence—followed by a reference 
to ‘‘ de engelsche tael”’ and “ de engelse kerck’’. 


verstaen’’, etc. etc. (in which en is now unnecessary and 
untranslatable): and the habit which Leeuwenhoek (not 
alone) had of dividing up his compound words into their 
constituents—e.g., he commonly wrote over geset, voort comen, 
al hoe wel, on na speurlijk, door gaens, etc., where we should 
now write overgezet, voortkomen, alhoewel, onnaspeurlijk, door- 
gaans, and so forth. 

Leeuwenhoek’s language appears, to me, to be full of 
philological interest ; but I am no philologist, and must there- 
fore content myself with noting some of the more obvious 
etymological and orthographic peculiarities of his writings. 
In my study of his manuscripts and printed letters I have 
been greatly aided not only by his contemporary translators 
but also by the lexicographers of his own period; and for 
the information of other students I therefore cite the chief 
dictionaries and other linguistic works which I have found 
most useful. Oudemans—the standard authority on Old and 
Middle Dutch—I have consulted only occasionally, on special 
points. Hexham, Hannot, and Halma have been of frequent 
assistance, while Kiliaan and Martinez and Minsheu have 
sometimes helped me over difficulties. Meijer’s Woordenschat 
(1745) contains numerous words which I have found in no 
other vocabulary : I should have used this valuable book more 
if I had known of its existence earlier. But my chief help, 
in translating Leeuwenhoek, has been the great dictionary of 
Sewel (1708)—a man’ who possessed a wonderful knowledge 
of the Dutch and English languages in Leeuwenhoeks time. 
This dictionary has been my constant aid during the last 17 
years, and I can confidently recommend it to anyone who 
wishes to know the exact Dutch and English equivalents of 

1 Willem Sewel (or William Sewell, as he would now be called in English) 
was born at Amsterdam in 1654. His grandfather was an Englishman, who 
married a Dutchwoman and settled in Holland. Sewel visited England as 
a boy, but lived most of his life in Holland, where he was first a weaver, 
then a journalist and translator, and finally the greatest of Dutch-English 
lexicographers. His parents were Quakers ; and in addition to his dictionary 
—which first appeared in 1691, and ran through several editions—he wrote 
a ‘‘ History of the Rise, Increase, and Progress’”’ of this sect (published in 
Dutch, 1717, and in English, 1722). Sewel died in 1720, aged 66. As he 
regarded himself as a Hollander, he would be pained to learn that his life 
is now to be found in our Dict. Nat. Biogr. but in no Dutch biographical 
works which I have consulted. 


words and phrases current in Sewel’s day. For modern Dutch 
and Dutch-English dictionaries I have relied in the main 
upon van Dale and ten Bruggencate, though I have frequently 
referred to other similar works. In common with all students 
of early English, I have received help at times from the well- 
known French Dictionary of Cotgrave, and Florio’s famous 
Italian-English vocabulary. The English dictionaries—of 
every period—which I have consulted, are all those to which 
I have had access: they are therefore far too numerous to 
mention. (I possess and regularly use more than a dozen.) 
As several old Dutch-English phrase-books and grammars, 
and the old Dutch Bible, have given me occasional assistance 
in arriving at the exact meaning of old-fashioned spellings 
ea I quote the editions of these which I have 

REFERENCES.—See, in the general bibliography at the 
end, the following entries especially : Anonymus (1658), 
de Beer & Laurillard (1899), Brenia (1702), Bosman 
(1928), ten Bruggencate (1920), Cappelli (1912), Cotgrave 
(1650), van Dale (1884), Florio (1688), Halma (1729), 
Hannot (1719), Heugelenburg (1727), Hexham, (1658, 
1660), Kiliaan (1599), Kilianus auctus (1642), Maigne 
d’Arnis (1890), Martinez (1687), Meijer (1745), Minsheu 
(1627), Oudemans (1869-1880), Sewel (1691, 1708, 1754). 


Leeuwenhoek left us no description of the apparatus which 
he used for making his observations on protozoa and bacteria. 
As we have already seen, he kept “for himself alone” his 
“best microscopes” and his “ particular manner of observing 
very small creatures.” He never divulged his secret method: 
though undoubtedly he had a real secret, which enabled him 
to outstrip all other microscopists for at least a century. But 
he left many microscopes behind him when he died, and a 
few of these are still in existence. Consequently, we know 
something about his apparatus, though we can still only guess 
how he used it in making his “ best observations.” 

The earliest particular accounts of Leeuwenhoek’s micro- 
scopes are the descriptions of the instruments bequeathed 


to the Royal Society.’ Martin Folkes," who examined 
Leeuwenhoek’s cabinet of microscopes shortly after it reached 
England, has left the following record”: 

The Legacy consists of a small Indian Cabinet, in the 
Drawers of which are 13 little Boxes or Cases, each 
containing two Microscopes, handsomely fitted up in 
Silver, all which, not only the Glasses, but also the 
Apparatus for managing of them, were made with the 
late Mr. Leewwenhoek’s own Hands: Besides which, they 
seem to have been put in Order in the Cabinet by him- 
self, as he design’d them to be presented to the Royal 
Society, each Microscope having had an Object placed 
before it, and the Whole being accompany’d with a 
Register of the same, in his own Hand-Writing, as being 
desirous the Gentlemen of the Society should, without 
Trouble, be enabled to examine many of those Objects, 
on which he had made the most considerable Discoveries. 

Several of these Objects yet remain before the Micro- 
scopes, tho’ the greater Number are broken off, which 
was probably done by the shaking of the Boxes in the 
Carriage. I have, nevertheless, added a Translation of 
the Register, as it may serve to give a juster Idea of 
what Mr. Leewwenhoek design’d by this Legacy, and also 
be of Use, by putting any curious Observer in Mind of a 
Number of Minute Subjects, that may in a particular 
Manner deserve his Attention. 

The 13 Cases abovemention’d are numbered from 15 
to 27 inclusively,’ corresponding to which is the Register 
of the Objects, Two to every Case, as follows. 

1 See p. 95 supra. As is well known, these instruments are now all lost. 
There is no foundation for the statement of Haeser (16532 Vol. I, p.a62* 
repeated in 3rd ed. 1881) that they are in the British Museum—nor have 
they ever been there, so far as I am able to ascertain. 

2 See p. 102, note 4, supra. 

° Holkes (1724), p.447 sq. L.’s own description of his cabinet has 
already been given on p. 96 supra. 

‘ Baker (1740, p.507), commenting on these numbers, says “it neces- 


No. 15. Globules of Blood, from which its Redness 

A thin Slice of Wood of the Lime-Tree, where 
the Vessels conveying the Sap are cut 

No. 16. [ Blank. | 

The eye of a Gnat. 

No. 17. A crooked Hair, to which adheres a Ring- 
Worm, with a Piece of the Cuticle. 

A small Hair from the Hand, by which it 
appears those Hairs are not round. 

No. 18. Flesh of the Codfish (Cabeljaeuw) shewing 
how the fibres lie oblique to the Membranes. 

An Embrio of Cochineal, taken from the Egg, 
in which the Limbs and Horns are con- 

No. 19. Small Pipes, which compose the Hlephant’s 

Part of the Crystalline Humour, from the Eye 
of a Whale. 

No. 20. A Thread of Sheeps- Wool, which is broken, 
and appears to consist of many lesser 

The Instrument, whence a Spider spins the 
Threads, that compose his Web. 

No. 21. A Granade, or Spark made in striking Fire. 

The Vessels in a leaf of Tea. 

No. 22. The Animalcula in Semine Masculino, of a 
Lamb taken from the Testicle, Jul. 24. 

A Piece of the Tongue of a Hog, full of sharp 

sarily implies there were 14 preceding Boxes, since no Man begins with the 
Number 15. Mr. Leeuwenhoek, then, had another Cabinet, that held 14 
Boxes before ours in numerical Order, and probably each Box contained a 
Couple of Microscopes, as our Boxes do.” 




No. 23. A Fibre of Codfish, consisting of long 
slender Particles. 
Another of the same. 
No. 24. A Filament, conveying Nourishment to 
the Nutmeg, cut transversely. 
Another Piece of the same, in which the Figure 
of the Vessels may be seen. 
No, 25. Part of the Bone or Tooth abovementioned, 
consisting of hollow Pipes. 
An exceeding thin Membrane, being that which 
cover’d a very small Muscle. 
No. 26. Vessels by which Membranes receive 
Nourishment and Increase. 
A Bunch of Hair from the Insect call’d a 
Hair- Worm. 
No. 27. The double Silk, spun by the Worm. 
The Organ of Sight of a Flie. 

For the Construction of these Instruments, it 1s the 
same in them all, and the Apparatus’ is very simple and 
convenient: They are all single Microscopes, consisting 
each of a very small double Convex-Glass, let into a 
Socket, between two Silver Plates rivetted together, and 
pierc’d with a small Hole: The Object is placed on a 
Silver Point, or Needle, which, by Means of Screws of the 
same Metal, provided for that Purpose, may be turn’d 
about, rais’d, or depress’d, and brought nearer or put 
farther from the Glass, as the Eye of the Observer, the 
Nature of the Object, and the convenient Examination of 
its several Parts may require. 

Mr. Leeuwenhoek fix’d his Objects, if they were solid, 
to this Silver Point, with Glew; and when they were 
Fluid, or of such a Nature as not to be commodiously 

" The reader will be better able to follow Folkes’s description if he here 

looks at my figure 1 on Plate XXXI, facing p. 328. 


view'd unless spread upon Glass, he first fitted them on a 
little Plate of Talk, or excessively thin-blown Glass, 
which he afterwards glewed to the Needle, in the same 
Manner as his other Objects. 

The Glasses are all exceedingly clear, and shew the 
Object very bright and distinct, which must be owing to 
the great Care this Gentleman took, in the Choice of his 
Glass,’ his Exactness in giving it the true Figure; and 
afterwards, amongst many, reserving such only for his 
Use, as he, upon Tryal, found to be most excellent. 
Their Powers of magnifying are different, as different Sorts 
of Objects may require; and, as on the one Hand, being 
all ground Glasses, none of them are so small, and conse- 
quently magnify to so great a Degree, as some of those 
Drops, frequently us’d in other Microscopes; yet, on the 
other, the Distinctness of these very much exceeds what 
I have met with in the Glasses of that Sort. 

Folkes gives no figures and no further information of 
material importance, though he makes the interesting state- 
ment that Leeuwenhoek had previously presented to Queen 
Mary, when she visited him at Delft, ““A Couple of his 
Microscopes, which, as I have been inform’d by one who 
had them a considerable Time in his Hands, were of the 
same Sort as these, and did not any ways differ from one of 
the 13 Cases contain’d in the Drawers of this Cabinet.” ® 

ss —  —  —— — —  — — —— 

‘This is a very shrewd remark. Undoubtedly L. knew a great deal 
about glass, and he was an expert glass-blower—as his recorded experiments 
prove. He learnt the art by watching a professional at the fair in Delft, 
and then practising by himself at home. 

* Mary II of England, wife of William III of Orange. She died in 
1694. Folkes calls her “the late Queen Mary,” and clearly did not mean 
her sister and successor, Queen Anne (died 1714). Halbertsma (1843, p.14) 
appears to have confused these two Queens when he says that L. was 
visited by “ Anna Maria.” 

* Folkes (1724), pp.450-1. Nothing else is now known about these 
instruments, which have long since vanished—like those presented to the 
Royal Society. 


The only other descriptions of the Royal Society’s micro- 
scopes were given some years later by Henry Baker‘ (1740,° 
1753), who determined their magnifying powers and—in his 
second publication—also gave two diagrammatic representa- 
tions of the instruments. Baker tells us that Leeuwenhoek’s 
microscopes were under his examination for three months,’ 
but he found Folkes had already given “ such an exact and 
full Description of their Structure and Uses, as renders any 
farther Attempt to that Purpose intirely needless.” * He 
notes that most of the objects before the glasses were even 
then (1740) “destroyed by Time, or struck off by Accident ; 
which indeed is no Wonder, as they were only glewed on a 
Pin’s Point, and left quite unguarded. Nine or Ten of them, 
however, are still remaining ; which after cleaning the Glasses, 
appeared extremely plain and distinct, and proved the great 
skill of Mr. Leeuwenhoek...’ He then makes the inter- 
esting further remark that Leeuwenhoek’s skill was also 
shown ‘in the Contrivance of the Apertures of his Glasses, 
which, when the Object was transparent, he made exceeding 
small, since much Light in that Case would be prejudicial ; 
But, when the Object itself was dark, he inlarged the Aperture, 
to give it all possible Advantage of the Light.” ’ 

But we are chiefly indebted to this verbose amateur for 
having carefully determined the focal length and magnifying 
power of every lens in the collection—notwithstanding he 

1 Henry Baker (1698-1774) was a Londoner, whose varied activities 
included dabbling in science. As a boy he was apprenticed to a bookseller, 
but later he made a fortune by teaching deaf mutes by a secret method of 
his own. In 1729 he married the youngest daughter of Daniel Defoe. He 
was elected F.R.S. in 1741, and by his will endowed the ‘ Bakerian Lecture ”’ 
of the Society. In early life he wrote much poetry and light literature. His 
chief contributions to science were two popular books on the microscope— 
mainly compilations, containing little original. In these works, which ran 
through many editions and were translated into several languages, he drew 
largely on L.’s letters. Cf. Dict. Nat. Biogr. and Rec. Roy. Soc. 

2 Though dated 1740, this paper must have been published considerably 
later: for it contains a reference to the 2nd edition of Baker’s Microscope 
Made Easy (1743: 1st ed. 1742), and he styles himself F.R.S.—to which he 
was not elected until 12 March 1741. 

* Baker (1753), p. 434 footnote. 
* Baker (1740), p. 504. 
° Baker (1740), p. 504. 


‘‘was sensible it must cost much Trouble.” ‘‘ This Task,”’ 
he says, ‘“I have performed, with as much care and Exact- 
ness as I was able.” His results were summarized in a table, 
which I here reproduce in full: * 

A Table of the Focal Distances of Mr. Leeuwenhoek’s 26 
Microscopes, calculated by an Inch Scale divided into 100 
Parts; with a Computation of their magnifying Powers, 
to an Hye that sees small Objects at 8 Inches, which is the 
common Standard. 

Micro- Distance Power of mag- Power of mag- 1 
scopes with of the nifying the Dia- nifying the ie 
the same Focus. meter of an Superficies. oN 
Focus. Object. 
Parts of an Inch Times Times 
ale so O goo ee ee AGOW: 5: 5,c on ke eae sO OOO > 
1: Fae eRe OR 133; nearly <9 )-ucva oso. 
1, TG) ene Meee 114) nearly:« <¢icccuansn ete 12996: 
3. FAG ORES tien LOO 3s, sas Yay edo 10000. 
3. Bera ht gessoi ag ck nal atlas 89! almost... cco useemes 7921 almost. 
8. Sep wee eu eaayts er. SO. sat «cise nee 6400. 
2. iro eC ee 72 something more... 5184 something more. 
3. eh oes She = 66 nearly’... 5". «eas 4356 nearly. 
2. Sea ota satet aie Diy! a Lay gsy chee eee 3249, 
al Se (AE aoa ee ae BS mearly, i.) cucseasas ss 2809 nearly. 
1. at Pee See a 40: ' 2S 2 ca eee 1600. 

* This largest Magnifier of allis in the Box marked 25. [Note by Baker. | 

Baker himself notes regarding these figures: “ I have given 
the Calculations in round Numbers, the Fractions making but 
an inconsiderable Difference; and I hope any Mistakes I may 
have made in so nice a Matter will be excused”. I must also 
note—since it has been generally overlooked—that all the 
magnifications are given for an image-distance (8 inches) 
which is not the “common standard” now universally adopted 
(10 inches). Consequently, all Baker’s “magnifying powers”’ 
represent only ~ of the actual magnification according to 
modern notation: and therefore the “largest Magnifier”, with 


1 Baker (1740), p.506. The later description (Baker, 1753; p. 436), 
though that usually quoted, gives far less detail. 


a focal length of 3G in., magnified not 160 but 200 diameters 
according to present-day reckoning—and so on throughout. 

After a somewhat lengthy discussion, Baker reaches the 
conclusion that Leeuwenhoek’s best microscopes, with which 
he made his most considerable discoveries, “ must certainly 
have been much greater Magnifiers than any in our Possession”’ 
—a conclusion which was then well founded. 

I need not give Baker’s illustrations of a Leeuwenhoek 
microscope—which have often been copied—nor their accom- 
panying description,’ for more instructive data are now avail- 
able: but I must here quote some other contemporary records 
which throw more light on the present subject. 

It is well known that Leeuwenhoek left many microscopes 
with his daughter when he died. Apart from the 26 bequeathed 
to the Royal Society there were some hundreds of others— 
though their number is generally misstated. Maria did not 
sell any of these instruments, but preserved them all her life. 
After her own death (1745), however, they were put up for 
auction and dispersed. Copies of the sale-catalogue (1747) 
are still extant ; but the late Professor P. Harting, of Utrecht, 
possessed a unique example which is of the greatest interest 
and on which he has left some valuable notes’. I shall 
therefore here translate his words verbatum, as they contain 
information now unobtainable elsewhere. In 1850 he wrote: * 

I have in my possession two copies of the catalogue 
of Leeuwenhoek’s microscopes, drawn up for the auction 
which took place on Monday the 29th of May, 1747. 
One of these copies was probably used by the notary or 
auctioneer at the time of the sale, for it is interleaved 
with white paper on which the names of all the buyers, 
and the prices fetched by the instruments, are carefully 
recorded. The catalogue is got up rather more luxuriously 
than is customary at the present day; for it is printed 

1 Baker (1753), pp. 434-436; Plate XVII, figs. VII and VIII. (Dutch 
edition [1770], pp. 453-456; Pl. XVII, afb. 7 & 8.) 

* Haaxman (1875), p.38, has also described this catalogue, but adds 
nothing material to Harting’s account. 

* Het Mikroskoop, Vol. III, p.41 footnote. I have been unable to 
discover what happened to Harting’s copies of the catalogue after his death. 


on heavy writing-paper, while a pretty allegorical copper- 
plate engraving is placed at the beginning, along with 
another displaying Leeuwenhoek’s portrait. The text is 
in Dutch and Latin both. 

From this catalogue it appears that Leeuwenhoek left 
no less than 247 completely finished microscopes, each 
provided with a lens, and generally also with an object ; 
and, in addition to these, 172 lenses merely mounted 
between little plates—419 lenses in all, therefore. 
Among these lenses there are three made from so-called 
‘Amersfoort diamond” (rock-crystal pebble)*; and of 
one of the microscopes it is noted that its magnifying- 
glass is ground from a sand-grain, while the object placed 
before it is likewise a sand-grain. ‘T'wo microscopes are 
specified as having two glasses, another three. It thus 
appears that Leeuwenhoek also manufactured doublets 
and triplets”; for, with his kind of apparatus, there can 
obviously be no question of any proper compound micro- 
scope. More than half of these microscopes (approxi- 
mately 160) were mounted in silver. Among the rest 
there are three made of gold—two of which weighed 
10 engels* 17 grains, the third 10 engels 14 grains. One 
of the former was sold for 23 florins 15 stivers, while both 
the others were bought in. (This is probably the only 
occasion on which microscopes have been sold by weight.) 
The remaining microscopes were sold in pairs. The brass 
ones fetched 15 stivers to 3 florins a pair, the silver 2 to 7 
florins. The entire sale realized a sum of 737 florins and 
3 stivers.t The names of the buyers show that all these 

i.e. quartz. I know of no evidence to show that L. ever made 
lenses from real diamonds—as is sometimes stated (e.g. by Nordenskidld, 
1929 ; p. 165). 

2 It now seems more probable that these were really double (or triple) 
simple microscopes—i.e. 2 (or 3) single lenses mounted in the same frame 
side by side—like the “double microscope” illustrated by Haaxman (1875) 
p. 34, fig. 2A. 

* An engels equals 32 grains: see p. 338 infra. 

* About £61. 10s. in modern English currency. 





microscopes were purchased by Hollanders,' and it is 
therefore surprising that one nowadays so seldom meets 
with any surviving specimens of Leeuwenhoek’s instru- 
ments in this country. 

Elsewhere Harting has published a list of the objects 

which Leeuwenhoek left fixed before his magnifying-glasses— 
as mentioned in the sale-catalogue. Though they include 
—like Folkes’s list—no protozoological or bacteriological 
items, they seem sufficiently interesting to quote. According 
to Harting, they were as follows: ” 

Animal Objects 

Muscle-fibres of a whale. 

a 59 99 COdLish. 

a ,, the heart of a duck. 
Transverse section of the muscles of a fish. 
Scales from human skin. 
Crystalline lens of an ox. 
Blood-corpuscles of a man. 

Liver of a pig. 
Transverse section of the bladder. 
Bladder of an ox. 
Papillae from the tongue of an ox. 
Hair of sheep. 

457 |, on DOAVEr. 

» 9» elk. 

wel Goss Dears 

» out of the [human] nose. 
Scale of a perch. 

»” »” > sole. 
Spinning-apparatus of a spider. 

Thread [web] 999» 
Sting ” 99 ” 
Teeth » » ” 
Hyes » ” 

Spinning-apparatus of a silk-worm. 

1 The names of all the purchasers (42 in number) have since been 
printed in Harting (1876), p. 33. 
2 Translated from Harting (1850): Het Mikroskoop, Vol. III, p. 465. 


Brains of a fly. 
Optic nerves of a fly. 
Tips of the feet of a fly. 
Sting and sheath of a flea. 
Feet » 9 99 
HKyes of a dragon-fly. 

» 99 beetle. 
Sting of a louse. 

MGM: 59 1 Sp of 
Ovipositor ,, 5, aa 
Red coral. 

Section of oyster-shell. 
Embryo oysters in a little [glass] tube. 

Vegetable Objects 

Transverse and longitudinal sections of elm-wood. 

” ” ” ” » fir-wood. 

»” ” ” »” »” ebony. 

»” »” ” » »” lime-wood. 
»” ” om) »” »” oak-wood. 
” » ” ” » Clnnamon. 
» » ” » »» cork. 

” » ” 5) » rush. 
Section of fossil wood. 

Germ out of the seed of rye. 

Vascular bundles out of a nutmeg. 

Mineral Objects 

Bits of white marble, rock-crystal, diamond, gold-leaf, 
gold-dust, silver-ore, saltpetre, crystals, etc. 

Harting was fortunately able to examine one of Leeuwen- 
hoek’s few surviving lenses carefully: and as his tests are the 
only recent ones made by an expert—so far as I am aware—I 
must here note what he found. He reports* that the biconvex 
lens which he studied was “really very good indeed”’, and 
proved that its maker had attained “a very high degree of 
proficiency in grinding extremely small glasses.” Its magni- 
fying power was no less than 270 diameters [indicating a focal 

1 Het Mikroskoop (1850), Vol. III, pp. 43, 44. 


length of about 0°9 mm.]: and its resolution was so good that, 
with suitable illumination, it was capable of resolving the 4th 
croup of lines on a Nobert test-plate (7.e., a scale 10 » long 
subdivided into 7 equal parts by parallel lines ruled with a 
diamond on glass). In Harting’s opinion this was probably 
the optical limit of Leeuwenhoek’s lenses: but the lens which 
he studied was only one of hundreds, and some of the others 
—now lost—may well have been superior.” 

Leeuwenhoek himself has—to my knowledge ’—left us no 
account of his particular procedure in making and mounting 
lenses. Others published their methods,* but he never did. 
How to grind and polish lenses for spectacles and telescopes 
was common property, however, at the time when he wrote; 
and it seems probable that he worked by the ordinary rules 
and with the customary apparatus. If you had asked him 
how to make a very powerful lens, of very short focus, he 
would doubtless have told you that it could only be made by 
the usual methods: but as such a glass would be much 
smaller, and more convex, you would have to do everything 
on a smaller scale, and pay more attention to details. If you 
can make a good lens with a focus of 1 foot, then you can— 
if you take pains, and know your job—make an equally good 
one with a focus of +$5 of an inch. It is more difficult, and 
takes longer; but that is all. It is a question only of the 
time and trouble that you are prepared to expend. The 
general methods of grinding and polishing lenses were no 
secrets: and when Leibniz asked old Leeuwenhoek why he 
did not educate a school of younger men in the art, he made 
the following reply :” 

1 Op. cit., Vol. I, p. 404. 

2 The lens examined by Harting was in a microscope preserved, at that 
date, in the physical collection at Utrecht. The instrument now in the 
zoological collection of the same university is greatly inferior—its lens 
having a focal length of about + in. (fide Mayall, 1886). 

* Crommelin (1929), in his recent admirable essay on lens-grinding [and 
lens-grinders] in the 17th century, is of the same opinion. On this subject, 
he says, L. “has left us entirely in the dark’’. 

* See especially Manzini (1660). 

> Send-brief XVIII, pp. 168-9 [Epist. Physiol. XVIII, p. 167]. Letter 
dated 28 Sept.1715. Not in Phil. Trans. 


To train young people to grind lenses, and to found a 
sort of school for this purpose, I can’t see there’d be much 
use: because many students at Leyden have already 
been fired by my discoveries and my lens-grinding, and 
three lens-grinders have gone there in consequence; to 
whom the students have repaired, to learn how to grind 
lenses. But what’s come of it? Nothing, as far as I 
know: because most students go there to make money 
out of science, or to get a reputation in the learned world. 
But in lens-grinding, and discovering things hidden from 
our sight, these count for nought. And I’m satisfied too 
that not one man in a thousand is capable of such study, 
because it needs much time, and spending much money ; 
and you must always keep on thinking about these things, 
if you are to get any results. And over and above all, 
most men are not curious to know: nay, some even make 
no bones about saying, What does it matter whether we 
know this or not ? 

In addition to Folkes’s and Baker’s and Harting’s des- 
criptions there are many other brief accounts and figures 
of Leeuwenhoek’s instruments. The first picture of his 
“microscope” is that introduced into Verkolje’s mezzotint 
(1686), in which Leeuwenhoek is depicted holding one in 
his own hand (see Frontispiece). A similar piece of apparatus 
is probably meant to be shown in the hands of the allegorical 
personages represented in two of the engraved titles to his 
works.' Baker (1753) gave, with his description, a couple of 
poor diagrams which have been copied over and over again— 
by Hoole (1807) and many others down to Disney (1928) and 
Bulloch (1930) at the present day. Uffenbach (1754) also 
pretended to portray ‘“‘ Leeuwenhoek’s microscope”; while a 
small but excellent figure (from an unknown example) was 
engraved on the title-page of the booklet by van Haastert 
(1823). Other pictures—sometimes accompanied by descrip- 
tions—are to be found in the works of Harting (1850), 

1 See Ontled. & Ontdekk. (1686) = Anat. s. Int. Rer. (1687): Vizfde 
Vervolg d. Brieven (1696) = Arc. Nat. Det. (1695). These engravings should 
also be found (somewhere or other) bound up in all the Dutch and Latin 
collective editions of L.’s letters. 



Haaxman (1871, 1875), Mayall (1886), Locy (1910, 1925), 
Sabrazes (1926), and divers other writers. ‘‘ Leeuwenhoek’s 
microscope’”’ has even appeared in a recent film, in a modern 
advertisement for a proprietary dentifrice, and in popular 
periodicals—such as the Dutch illustrated weekly De Prins, 
which lately published (38 January 1925) the best photograph 
which I have yet seen. 

Although Leeuwenhoek made and left many microscopes, 
nearly all of them have long since disappeared. Not only have 
those bequeathed to the Royal Society vanished without 
trace, but even some of the few other examples mentioned 
by Haaxman and Harting—still surviving in 1875—cannot 
now be found. According to my friend Professor Crommelin 
(1929a) only 8 specimens in all are now known to exist, 5 of 
which are in Holland. Of these, 1 is in the Zoological 
Institute at Utrecht, and 3 others were, until recently, in the 
private possession of Mr P. A. Haaxman at The Hague: but 
2 of the latter have now passed into the Historical Scientific 
Museum at Leyden, and have thus become the property of the 
Dutch nation.” (All three were exhibited at a congress in 
Leyden in 1907. Cf. van Leersum, de Feyfer, and Molhuysen, 
pp. 114, 115.) Iam informed that two other genuine instru- 
ments are now in Germany—one in a well-known museum, 
the other in the possession of an optical firm: but I have not 
yet been able to verify these statements. I have also been 
told* that the late Dr Henri Van Heurck, of Antwerp, had an 
authentic specimen of Leeuwenhoek’s handiwork in his collec- 
tion which was sold in 1914. The Nachet Collection (Paris) 
also claims to possess one.* Neither in England nor America, 

1 There seems to be a general suspicion—probably fostered by some 
injudicious remarks of Saville Kent (Vol. I, p. 9, footnote)—that Baker, the 
last man known to have handled these instruments, was in some way 
responsible for their disappearance. This is entirely unjustifiable: for a 
search through the Society’s records (made on my behalf by Mr A. H. 
White, our learned librarian) has shown that we still possessed L.’s micro- 
scopes long after Baker’s death. They vanished from the Royal Society’s 
collection only about a century ago, and the few remaining records appear 
to incriminate a very different person. 

2 Cf. Crommelin (1929a). 

* By Mr W. E. Watson Baker, who—with his father—valued the 
collection before the sale. 

* The Nachet Catalogue, I may remark, is grossly inaccurate in nearly 


however, is there any genuine specimen (so far as I have been 
able to ascertain), though modern facsimile reproductions are 
now in circulation in both these countries. These copies are 
accurate, and some of them may before long be passed off as 
authentic originals. More than one such exact facsimile was 
made for the late Sir Frank Crisp, who preserved one example 
in his private collection and presented another to the Royal 
Microscopical Society of London (on 21 January 1914), in 
whose rooms it can now be seen.’ Crisp’s own facsimile was 
sold at Stevens’s in London on 17 February 1925, when 
his collection was auctioned after his death.” Other similar 
reproductions are also in existence. One was recently in 
California, and a friend of mine (who saw it) states that its 
owner assured him that he could obtain similar “‘ Leeuwenhoek 
microscopes”’ at any time—for a price—from Holland. Be 
this as it may, there are certainly facsimiles (and forgeries ?) 
now on the market, and prospective purchasers should be on 
their guard. 

Most of the recent descriptions and pictures of “ Leeuwen- 
hoek’s microscope” are based on the rather poor specimen 
now preserved in the Zoological Laboratory at Utrecht. The 
best account and figures*® of this instrument are, I think, 
those of Mayall (1886): but as I am not wholly satisfied with 
his or any other description or pictures (Mayall, apparently, 
never saw the microscope which he described), I shall here 
attempt to revise his version with the help of a few drawings 
of my own. My account is based on personal examination of 
three genuine specimens, one copy, and a study of all other 
available data. I must point out, however, that my own 
figures (Plate XXXI) were not drawn from any actual 
instrument. They form a composite design—a generalized 

2 ___ aa 

all its references to L. (see Nachet, 1929). I have not seen the instrument in 
this collection; but from the description and picture it appears suspiciously 
like one of the recent copies of the Utrecht example. 

1 Of. Disney (1928), p.160. This instrument is evidently a copy of 
the original now in the Zoological Institute at Utrecht, and most of the 
other copies appear to have been made from the same example. One such 
has been figured recently by Becking (1924). 

2 See the Catalogue of this sale, Lot 1. 

* Woodcuts, made directly from photographs. These excellent figures 
have recently been reproduced (as line blocks) by Disney et al. (1928, 
Plate 1) without acknowledgement. 


representation of ‘“‘a Leeuwenhoek microscope ’"—embodying 
all the features common to the extant examples. I have 
tried to show the mechanism as simply as possible and with 
the fewest and most easily comprehensible drawings, because 
I find all previous accounts incomplete, inaccurate, or difficult 
to understand. Several describers, indeed, do not themselves 
appear to have grasped the mechanism—either literally or 
metaphorically. My drawings are based primarily on the 
microscopes formerly in the possession of Mr P. A. Haaxman 
(The Hague), whose daughter—Mejuffrouw S. A. E. Haaxman— 
very kindly permitted me (on 29 June 1923) to take one of 
these priceless little instruments to pieces, sketch the various 
parts, and reassemble it. For the accuracy of my description 
I rely chiefly upon the notes and tracings which I made on 
this occasion. Unfortunately I have had no opportunity of 
testing any of Leeuwenhoek’s lenses. 

All Leeuwenhoek’s microscopes had an appearance like 
that shown in Plate XXXI, fig. 1. Properly speaking, they 
were not “microscopes” at all, but—as he himself usually 
called them—simple “ magnifying-glasses”. Hach consisted 
of a single biconvex lens (not a system of lenses); and the 
mechanical parts were contrived not to focus this lens upon 
an object lying on a fixed stage (as in a modern compound 
microscope), but in order to bring a movable object into the 
focus of the glass, which was itself fixed. It is important to 
realize this fundamental point in the design, which is highly 
original. It should also be emphasized that all these instru- 
ments were very small—even smaller than my drawings. 
They were generally made of the same metal throughout, 
though different metals were used (brass, copper, silver, and 
even gold occasionally): and the workmanship and finish 
were none too good. Leeuwenhoek concentrated his attention 
upon the optical part of his “microscopes” : and when he had 
succeeded in grinding and polishing and mounting a good lens, 
he evidently did not think it worth while to spend a lot of 
time in finishing off its mechanical accessories, which were 
made just.good enough for his purpose. 

Fig. 1 (Plate XX XI) shows the whole instrument from the 
back, as fitted up ready for use. Figs. 2 and 3 illustrate details ; 
and ‘fig. 4 is a diagrammatic longitudinal section. These 
drawings will, I hope, almost explain themselves— if carey 
studied ; but I may add the following notes : 






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The minute biconvex lens (J, fig. 4) was mounted between 
two thin oblong plates of brass (or other metal). Towards 
one end of each plate, at the same point in the middle line, a 
concavity was ground or punched and a hole pierced in its 
centre. When these apertures had been made to coincide 
exactly, the lens was clamped between the plates, in the 
concavities (as shown in fig. 4), and secured by four equidistant 
rivets forming the corners of a square (see fig. 1) with the lens 
at its centre. In other words, the rivets and the lens—in 
surface view—formed a quincunx, the lens occupying the 
central spot. 

The two oblong metal plates’ with the lens thus mounted 
between them constitute the essential optical part of the 
instrument. Leeuwenhoek probably kept many of his lenses 
so mounted, and fixed interchangeable mechanical parts to 
them as required. These mechanical accessories— for focussing 
the object before the lens-—are shown in the figures and have 
been well described by Mayall in his Cantor Lectures (1886) 
as follows: ‘“‘ The object is held in front of the lens, on the 
point of a short rod, the other end of which screws into a 
small block or stage of brass [whose peculiar shape is shown 
from above in fig. 2], which is rivetted somewhat loosely on 
the smoothed cylindrical end of a long coarse-threaded screw 
[figs. 1, 4] acting through a socket angle-piece | fig. 3] attached 
behind the lower end of the plates by a small thumb-screw 
[s, fig. 4. Only the projecting end of this screw is visible 
in fig. 1. It is furnished with a roughly-fashioned metal 
washer above the angle-piece—shown in section in fig. 4]. 
The long screw serves to adjust the object under the lens in a 
vertical direction, whilst the pivoting of the angle-piece [fig. 3] 
on its thumb-screw [fig. 4, s] gives lateral motion. ‘The 
object-carrier can be turned on its axis, as required, by 
screwing the rod into the stage [by means of a metal knob, 
shown in figs. 1 and 4. When the rod is rotated by moving 
the knob, the object is not only turned on its axis but raised 
or lowered by the screw passing through the block—thus 
forming a sort of “fine adjustment” for the “coarse adjust- 
ment” provided by the long screw]. For focussing, a thumb- 

1 The brass lens-holding plates of the best Haaxman specimen measure 
approximately 41 mm. by 18 mm.; but their sides are not accurately 
parallel, and their corners are roughly rounded. 


screw passes through the stage near one end [figs. 1, 2,4], and 
presses vertically against the plates, causing the stage to tilt 
up at that end; the fitting of the long screw-carrier (angle- 
piece [fig. 3]) is such that the stage at the end is sprung 
down somewhat forcibly on the brass plates, and it is against 
this pressure that the focussing screw acts.” 

As we have already heard, the object to be viewed was 
either stuck directly on to the pin of the object-carrier, or 
else it was first mounted in some way (¢.g.,on a small plate of 
glass or mica, or between two thin glass plates like a modern 
slide and coverslip, or in a capillary glass tube) and the whole 
was then fixed and focussed before the lens. A “ microscope” 
of this type, with a lens of very short focus and high magni- 
fication, must have been extremely awkward to manipulate. 
It would be necessary to place the eye almost in contact with 
the lens, and it is not clear how Leeuwenhoek was able to 
obtain the requisite illumination. The known magnifying 
power of his best glasses was, of course, sufficient to enlarge 
objects as small as blood-corpuscles (and even bacteria) to 
visually perceptible dimensions—a fact which modern workers 
with the compound microscope seem apt to overlook. With 
the front lens of my 2 mm. apochromatic objective—having a 
magnification of about 120 diameters—I can distinctly see 
(using the light of a clear sky only) bacteria as small as 
Bacillus coli in a stained film. But to see such organisms 
alive in water, and with sufficient clarity to describe their 
movements, is another matter. (My own eyesight, I should 
note, is exceptionally good—probably but little inferior to 
Leeuwenhoek’s.) Yet Leeuwenhoek not only knew how to 
make lenses of adequate magnifying power and aperture and 
resolution, and sufficiently free from spherical and chromatic 
aberration, but he also understood how to obtain the necessary 
visibility. He was able,in some way, to get the indispensable 
contrast between the object and its background which we 
now readily obtain by means of central stops, iris diaphragms, 
or staining. 

It appears to me certain, indeed, that Leeuwenhoek cannot | 
have made his extraordinarily accurate observations on bac- 
teria and protozoa by means of the apparatus just described 
when used in the ordinary way. He had unbounded patience 
and magnificent eyesight—as his works abundantly testify— 


but he could not perform miracles. Moreover, there is no 
reason to suppose that he possessed any apparatus essentially 
different from that which is now known. (Blanchard’s sug- 
gestion (1868) that he destroyed his best instruments in his 
old age “with the idea of continuing to appear to everybody 
as an incomparable observer ”’, is. quite unjustifiable.) All the 
evidence indicates that it was the method of using this appar- 
atus which he ‘“‘ kept for himself alone’”’: his secret lay, as he 
tells us repeatedly, in his “ particular method of observing.” 
What can it have been? The answer is—to me—almost 
certain, though I cannot prove from his own words (since he 
tried not to give his secret away) that I am right. I am 
convinced that Leeuwenhoek had, in the course of his experi- 
ments, hit upon some simple method of dark-ground wllwmin- 
ation. He was well aware, as we know, of the ordinary 
properties of lenses; and he tells us himself that he used 
concave magnifying mirrors and employed artificial sources 
of illumination (e.g. a candle). Consequently, he may well 
have discovered by accident—or even have purposely devised 
—some method which gave him a clear dark-ground image. 
Such a discovery—possibly inspired by observing the motes. 
in a sunbeam—would at once explain all his otherwise inex- 
plicable observations, without supposing him to have possessed 
any apparatus other than that which we now know he had. 
But no hint was ever knowingly given, in all his many letters 
(so far as I have been able to ascertain), of what his “ par- 
ticular method of observing” may really have been. 
Nevertheless, there is, in a very early letter, a remark 
which seems to me to substantiate my interpretation—though 
one must, I think, be personally familiar with such things to 
appreciate it properly. Writing about red blood-corpuscles in 
1675, Leeuwenhoek (in reply to criticism) says :* 
. . . but I can demonstrate to myself the globules [= cor- 
puscles] in the blood as, sharp -and clean as one can 
distinguish with one’s eyes, without any help of glasses, 
sandgrains that one might bestrew upon a piece of black 
taffety silk. 

1 From Letter’ 9. 22 January 1675. To Oldenburg. MS.Roy.Soe. 

* The words I have here interpreted and italicized are, in the original, 
“desantgens . . . diemen op een swart sijde taff ‘soude mogen werpen”’. 


Taffeta (formerly taffety or taffata—a word of Persian 
origin) is a name now applied to various coloured fabrics of 
wavy lustre: but in earlier times it denoted a silken cloth of 
uniform texture—when black, much used for mourning. It 
should be remembered that Leeuwenhoek speaks here not 
only as a microscopist but also as a draper; and he therefore 
meant that he could see human red blood-corpuscles under his 
microscope just as clearly as he could see sandgrains scattered 
on a piece of the smooth black silk he sold in his shop. The 
more I consider these words, the more am I convinced that 
nobody could ever have thought of such a simile unless he 
had seen red corpuscles under dark-ground illumination. 
Their appearance by transmitted light is wholly different, and 
could never suggest such a comparison. To my mind these 
words furnish an almost conclusive proof that Leeuwenhoek’s 
“particular method of observing very small objects” was 
some simple system of dark-field lighting, used in combination 
with his ordinary microscopes. It is idle to speculate on how 
he may have achieved this result : it is sufficient to note that 
such a supposition will easily explain all his otherwise inex- 
plicable observations. (It readily explains, for instance, how 
he was able to see flagella and cilia and spirochaetes and 
micrococci with a magnification of only some 200-300 dia- 
meters.) But as he himself would say, “I hand this notion 
over to others.” 

Leeuwenhoek’s apparatus for viewing the circulation in 
the tail of an eel was fully described and illustrated by 
himself.’ It is a peculiar instrument, designed for a special 
purpose, and not his “‘ microscope”? proper—though it has 
more than once been figured as such by later writers. I need 
not consider it here. I may note, however, that one of these 
instruments is now in the Leyden Museum (with some lenses 
made and mounted for it by himself, and a copy by another 
maker). Leeuwenhoek’s own figures” show that he sometimes 
used the lenses of his “ microscopes’”—mounted between two 
oblong metal plates, as already described—in fitting up this 

1 Letter 66. 12 January 1689. To the Royal Society. Printed in Dutch 
and Latin works, but not in Phil. Trans. The original is preserved among 
the Boyle MSS. of the Royal Society. 

* See especially fig. 8, on the plate accompanying this letter. 


apparatus. His magnifying-glasses were evidently so designed 
that they could be used interchangeably for ‘ microscopes ” 
or ‘‘enchelyscopes”’, as occasion required, by adding the 
appropriate mechanical parts. 

I may also note here that Leeuwenhoek was one of the 
first—if not the very first—to study the structure of solid 
opaque bodies by means of sections. Some which he cut 
with his own hand “by means of a sharp shaving razor ” are 
still in existence. They were enclosed in a little packet 
affixed to an early letter,’ and have remained intact to the 
present day. According to his own description, they are 
(1) “Cork”; (2) ‘‘ White of a writing pen” [parings from a 
quill] ; (3) “ Bits of the optic nerve of a cow, cut crosswise ”’ ; 
(4) “ Pith of elder.” He added the following suggestions for 
looking at these objects : 

: I would venture to recommend that, when one 
of these sections has been brought upon the pin of a 
microscope, you then hold the microscope towards the 
open sky, within doors, and out of the sunshine, as though 
you had a telescope and were trying to look at the stars in 
the sky through it. 

LEEUWENHOEK’S MicroMEtRY.—Before the invention of 
micrometers it was extremely difficult to measure very small 
objects under the microscope: their size could, indeed, be 
only estimated, by reference to other objects of known dimen- 
sions. On an earlier page” we have read Leeuwenhoek’s 
own account of the way in which he assessed the probable 
magnitude of various animalcules, but a few further notes are 

Leeuwenhoek took the inch_(of his land and period) as an 
absolute unit for small measurements. A copper rule,’ with 

1 Letter 4. 1 June 1674. To Oldenburg. MS.Roy.Soc. Partly published 
in English in Phil. Trans. (1674), Vol. IX, No. 106, p.121. L. also sent a 
copy of this letter to Const. Huygens, and this copy—now in the Leyden 
library—has recently been printed in its original Dutch by Vandevelde and 
van Seters (1925). 

* See p. 201 seq., supra. 

3 Referred to on p. 189 supra. 


the inches subdivided into tenths, was his standard. Fortu- 
nately, he had this engraved for one of his later letters,’ so 
that it can now be measured. From the picture it appears 
that his “ inch’”’ was approximately 26°15 mm., and therefore 
slightly greater than the modern English inch (25'4 mm.).” 
His own drawing of a cubic inch (p. 189 supra) confirms 
this determination. 

The commonest objects with which Leeuwenhoek com- 
pares ‘“‘animalcules” are a sandgrain, a human red_blood- 
corpuscle, a vinegar-eel, and a millet seed. He also used 
other more or less verifiable measures, however, such as “a 
hairsbreadth,” “‘the diameter of a louse’s eye,” “the bigness 
of a hair on a louse,” etc. J may say a word on each of these. 

Sandgrains are Leeuwenhoek’s common standard of com- 
parison. At first sight it seems impossible to translate these 
highly variable structures * into exact modern measurements, 
but it is actually—from the information which he supplies— 
quite feasible. He generally referred to two kinds of sand— 
coarse and fine. A fine sandgrain, according to the letter 
translated on p. 188, was about #5 inch in diameter : but else- 
where‘ he states that 100 of his very small sandgrains, laid 
end to end, equalled about an inch. This seems to be the 
usual magnitude he had in mind—7.e., about 745 of an inch, 
or (using his scale) approximately 2604. A coarse sandgrain, 

according to his own statement,’ was about 35 inch in 

1 Send-brief XXVIII, to Boerhaave. 28 September 1716. Also published 
in Latinin Epist. Physiol. and Op. Omn. The plate faces p. 271 of the Dutch 
edition, and p. 266 of the Latin. 

2 The scale in the figure is 5 inches long, and is accurately delineated. 
A fair average can therefore be readily obtained for 1 inch. But as the 
actual engraving was made on copper, and the prints are on paper (which 
was wetted, and then shrank somewhat), I have made my estimate from 
4 different prints in my possession (which differ only very slightly from one 
another). The mean for 1 inch (here given) is therefore derived from the 
combined measurements of 20 printed inches. 

3 Ty. said himself (Send-brief XLI, 26 Aug. 1717) that “as big as a grain 
of sand” is an inaccurate expression, andit would be better to use a millet 
seed or a mustard seed for comparison. 

4 Letter 35, to R. Hooke. 3 March 1682. Published in Dutch and 
Latin works. 

> Letter 42, to the Royal Society. 25 July 1684. Published in Dutch 
and Latin works. 


diameter, and therefore some 870 ». These magnitudes seem 
to agree well with all Leeuwenhoek’s inferences—so far as 
I have been able to check them. 

A Red Blood-corpuscle (of man) measures about 7°5 u 
in diameter, and Leeuwenhoek’s frequent choice of this 
structure as a standard of size has been amply confirmed by 
all later microscopists. Even today we commonly see an 
outline of a human erythrocyte inserted among drawings 
of microscopic organisms as an indication of their relative 

It may be remarked here that Leeuwenhoek himself had a 
very good idea of the actual diameter of a red corpuscle, though 
he could not express it exactly in terms of any micrometric 
unit : for he notes in one place’ that he had satisfied himself 
that 100 diameters of a red corpuscle amounted to something 
less than that of a coarse grain of sand (which he had just 
assessed at 35 inch). Consequently, he imagined the diameter 
of a corpuscle to be rather less than 3500 of an inch—an~ 
astonishingly good estimate.” 

The Vinegar-Hel (the nematode Anguillula aceti) is 
assigned various sizes in the text-books. I have cultivated 
and studied this worm at various times, and find that ordinary 
large individuals (females) may measure anything from about 
1200 to 1700 in length. “A full-grown eel such as we 
see in vinegar’”’ is approximately 1°51um. long, and this agrees 
quite well with all Leeuwenhoek’s references. 

A Millet Seed is more difficult to appraise. There are 
now many kinds of millet (Panicum miliaceum)—*a name 
applied with little definiteness to a considerable number of 
often very variable species of cereals, belonging to distinct 
genera and even subfamilies of Gramineae”’.* I have measured 

1 Letter 42, p. 32 of Dutch edition. 

* This was pointed out by Harting in 1850 (Het Mikroskoop, III, 404), 
and again by myself (1920)—in ignorance of his earlier annotation. 
Haaxman (1875, p.56) makes the absurd mistake of commending L. for 

estimating the diameter at so (instead of goo) of an inch. 

3 Encyclopaedia Britannica, 11th ed. (1911). It is rather surprising that 
“a, millet seed” is still so frequently referred to, as a standard of size, in 
biological writings (especially text-books). I have asked many people how 
big a millet seed is, but have never yet found anybody who could tell me 
even approximately—including one distinguished person who had himself 
used the expression as a descriptive term. 


samples of modern “ brown” and “ white ” millet (commonly 
sold for bird-seed) and found that the grains averaged 1°8 mm. 
and 2:17 mm. respectively: but as they are not spherical, 
their “diameter” is difficult to determine. In one place’ 
Leeuwenhoek estimates a green pea to have a diameter equal 
to 4} millet seeds, while elsewhere” he says that a pea weighs 
8 grains. On selecting a few fresh green peas of about this 
weight (520 mg.) and measuring them, I found their diameters 
‘to be rather less than lem. (But here again—as peas are 
not round—it is impossible to express their diameter, or 
“axis”? as he called it, with precision.) If Leeuwenhoek’s 
millet had a diameter of about # of such peas, it must have 
measured roughly 2mm. across. This agrees with my 
estimates from modern millet, and does not seem to disagree 
with any of his own statements. I assume, therefore, that 
when he uses “a millet seed” as his standard, he means a 
spherical body approximately 2 nm. in diameter. 

A Hairsbreadth is estimated by Leeuwenhoek himself? as 
equal to g3o of an inch (about 43°6 w on his scale). The hairs 
measured were plucked from his wig—not his own head—and 
human hairs are usually much coarser.” 

The Eye of a Louse’ appears to be rather an indefinite 
standard of size. I find, however, that it can be estimated 
approximately. The eyes of Pediculus humanus corporis (the 
louse which Leeuwenhoek particularly studied) have fairly 
uniform dimensions in both sexes. They are not spherical; 
but series of measurements made longitudinally and trans- 
versely give closely similar mean diameters. The average for 
‘an eye of a big louse’’ I have found to be about 70 u—ranging 
from 64 » to 80 w. It can thus be said, with a fair approxima- 
tion to the truth, that ‘‘a louse’s eye’ has a diameter 10 times 
that of a human red blood-corpuscle. This is in good agree- 
ment with Leeuwenhoek’s interpretations. 

1 See p. 169 supra. 

> See p. 214 supra. 

3 See p. 189 supra. 

+ Most of my own hairs, which are unusually fine, have diameters at 

least twice as great. I have never seen a human hair (from the head) 
measuring only 43 u in diameter; but I have made no extensive investigation 
of this matter—being content with L.’s own statement. 

> Of. p. 121 et alibi, supra. 


A Hair on a Louse is a less accurate comparison: for the 
setae on P. corporis vary greatly in diameter, in different parts 
of the body. Moreover, they all taper to a point, so that their 
sides are not parallel. Large hairs, I find, have a maximum 
width of about 4 »: but smaller ones measure only 2°5 w or 
even less. “The thickness of the hairs wherewith the body 
of a louse is beset” I estimate—very roughly—to be something 
more than 3 yp. 

I can add little else to what Leeuwenhoek himself tells us 
about his micrometry.' I may mention in conclusion, how- 
ever, that he had some correspondence on the subject with 
Dr James Jurin in the last year of his life. Jurin, in 1718, 
invented” a new method of measuring small objects ; and in 
1722 he wrote to Leeuwenhoek about it, and persuaded him 
to try it. Leeuwenhoek did so, and his answering letter was 
published.’ Though it is not generally known, Jurin’s own 
draft (in English) of his letter to Leeuwenhoek is still extant. 
It is an interesting letter, and its present owner* has kindly 
allowed me to read and copy it: but asit has no bearing upon 
Leeuwenhoek’s own methods, I need not print it here. 

Finally, I may note that the we:ghts mentioned by 
Leeuwenhoek, in various letters, sometimes furnish clues to 
his measurements. We could, indeed, exactly determine some 
of his small measures of length if we knew the exact equivalents 
of his weights in modern units. We do not know, however, 
how closely his “grain” or “ounce” agree with modern 
weights of the same name; though fortunately he recorded his 

1 Tt should be noted that an earlier attempt to evaluate L.’s measure- 
ments was made by Muys (1741; p.332, note 72). His words are worth 
consideration ; but his estimates can hardly be regarded as satisfactory at 
the present time, so I shall not discuss them here. 

2 See Jurin (1718). His method was simple and ingenious. It consisted 
in closely winding fine hairs or silver wire on a needle, along a measurable 
length, and then determining the diameter of the hair (or wire) by counting 
the number of turns in that length. The diameter of the filament being 
thus ascertained, it was cut into small bits and strewn among the objects to 
be measured, whose size was estimated (under the microscope) by comparison. 
In this way Jurin determined the diameter of a human red blood-corpuscle 
to be gz'z5 inch (a very close approximation). 

3 Phil. Trans. (1723), Vol. XXXII, No. 377, p.341 (MS.Roy.Soc. 
19 March 1723). 

4 Mr A. K. Totton, a kinsman of Jurin and a former pupil of mine. 


own “table of weights ” himself, so that we know their relative 
values. Writing to Tschirnhausen * in 1699 he says:° 

Over here we divide a pound |pont] into 16 ounces 
[oncen], and each ounce into 20 engels,* and each engels 
into 32 grains [asen]; and consequently, then, a grain 
[aas] is todz0 Of a pound. 

Tt is thus clear that Leeuwenhoek’s “grain” (aas), which 
was gto of his ounce, can hardly have been identical with our 
modern grain (4373 = 1 ounce, or 7,000 = 1 Ib. avoirdupois). 
Wherever I translate “asen” as “ grains”, in the foregoing 
pages, it is merely for want of any other term ; and the reader 
will therefore please bear in mind that Leeuwenhoek’s * grain ” 
was only approximately the weight nowadays called by the 
same name in English (1 grain=0°065 gramme). But these 
are problems for the expert metrologist—not for a poor 
protozoologist or bacteriologist—and their further discussion 
is beyond my competence. 


The tragicomical history of Leeuwenhoek’s house in Delft 
has never yet been fully related, but it deserves notice here 
for several reasons. ‘These are the facts, so far as I have been 
able to ascertain them. My information is derived chiefly 
from Soutendam (1875), Haaxman (1875), Harting (1876), 
Bouricius (1924, 1925), and an anonymous article” recently 
published in the Wereldkroniek—supplemented by a few 
personal observations and inquiries made on the spot in 1923. 

In September 1875 an international celebration of “the 
200th Anniversary” of Leeuwenhoek’s discovery of the 
“Infusoria’”’ was held at Delft. (Harting [1876] records the 
events which led up to this congress.) The fixing of the date 
of the original discovery on September 1675 was, as we now 

1. W. von Tschirnhausen (1651-1708), the well-known German 

2 Letter 120, dated“. . . 1699.” Published in Dutch and Latin 
collective works. See p.131 of Dutch edition. 

* There is no English equivalent of this word. 

4 See Anonymus (1909). 

know, incorrect: nevertheless, the “ anniversary”? was duly 
celebrated on the date erroneously determined—to the evident 
satisfaction of all participants. By that time everyone had 
forgotten where Leeuwenhoek had lived: but the then 
archivist of Delft (Mr J. Soutendam) endeavoured to find 
out, and he finally pitched on an old house standing at 
the corner of Oude Delft and the Boterbrugstraat (not 
‘“ Botersteeg”’, as Haaxman called it). An “ astrolabiwm” or 
“planetarium” still present by the doorstep (figured by 
Soutendam, 1875) was taken to confirm his identification of 
the site—this bit of “scientific apparatus” presumably indi- 
cating that the house in question had once been occupied by 
a man of science. Even at that date (1875), however, the 
house itself was, by all accounts, much restored and altered. 

As Leeuwenhoek’s habitation had been thus identified, the 
“anniversary ’’ celebrations included a visit of the delegates 
en masse to this hallowed spot. The tenant of the house at 
that time (Mr J. B. A. Muré) received them graciously: he 
also allowed a stone memorial slab to be affixed to the front 
of his residence, and bound himself legally to be responsible 
for its future preservation. (The agreement is printed in 
Harting, 1876; p. 89.) 

So far so good. Some years later, however, the tenant of 
the house died, and it passed into the hands of a builder at 
The Hague who inconsiderately ordered it to be demolished. 
By that date (1892) everybody had, apparently, forgotten all 
about Leeuwenhoek again: but when the house came to be 
pulled down, the stone block bearing his name, and the 
‘‘ planetarium ” by the steps, were noticed. They were there- 
fore preserved, consecrated with the seal of the municipality, 
and deposited (on 3 December 1892) in the Municipal Museum 
at Delft—where they now repose. (The memorial tablet is 
an oblong block of white marble bearing the words Antony 
capitals. The “planetarium” is a decorative iron railing 
bearing no obvious resemblance to any scientific instrument.) 
The site occupied by the house was not built on, but was 
converted into a playground for the girls’ school adjoining 
(the Meisjeshuis, erected in 1760); and again everything was 

Some 17 years later, a local society called “ Delfia”— 
concerned with the improvement of the town, and the preser- 


vation of its antiquities—realized that something ought to be 
done to commemorate Leeuwenhoek in the place of his birth, 
residence, and death. They therefore instituted a competition 
in which artists were invited to submit designs for a suitable 
memorial. ‘The winning entry was duly accepted and erected 
—a bronze shield,’ showing a bas-relief bust of Leeuwenhoek 
(modelled on Verkolje’s portrait) with a Dutch inscription, 
executed and signed by J.C. Schultsz. It is still stuck on the 
railings surrounding the school playground, where it was 
affixed in 1909. Apart from his tomb, this is still the only 
monument to Leeuwenhoek in Delft. 

But more recent research into the town archives—made 
by a later and more critical archivist, the late Mr L. G. N. 
Bouricius—has proved that Leeuwenhoek never lived on the 
spot where his modern bronze effigy with its false inscription 
now hangs. His real residence was in a neighbouring street 
—the Hippolytusbuurt—and has long since vanished without 
trace. Consequently, all the belated local endeavours to 
commemorate Leeuwenhoek have been futile. It is certain 
that he never lived on the spot where the delegates were 
thrilled in 1875, and where his memorial now incongruously 
stands: nor did he make the supposed discoveries in the year 
therein alleged. His own house—where he lived and laboured 
and died—was in a different street, and has long since been 
destroyed by his forgetful fellow-townsmen. ‘The railings 
adorning another man’s doorstep—now preserved in the 
Municipal Museum of Delft—are a worthless object which 
would surely have excited his derision. 

Before the celebrations of 1875 were held in Delft, invita- 
tions were issued by the organizing committee to every body 
and everybody likely to be interested. Yet England—almost 
alone—made no response. The Royal Society, indeed, not 
only sent no delegate, but even failed to acknowledge their 
invitation: and England and London and the Royal Society 
thus placed themselves—to quote Harting (1876)—“on a 
level with Spain and Portugal and Greece.” We ought, 
undoubtedly, to have taken some part in commemorating 
Leeuwenhoek’s discoveries, with which we were so intimately 
concerned: yet our disgrace is now, perhaps, mitigated by 

1 Figured in the anonymous article in the Wereldkroniek (1909). A 
plaster cast is also preserved in the Museum at Delft. 


the accidental circumstance that no Englishman or Fellow of 
the Royal Society was present at the farce enacted in 1875 at 
‘* Leeuwenhoek’s house, where he discovered the Infusoria in 
1675”. But the whole affair is deplorable, and the less said 
about it the better. 

The comedy of errors associated with ‘ Leeuwenhoek’s 
house ” is unhappily paralleled in the history of his birthplace. 
About ten years ago, Mr Bouricius succeeded in discovering 
the place where Leeuwenhoek was born—a house in the 
Oosteinde of Delft, at that date still erect but used as a 
warehouse by a hide-merchant named Roes. Bouricius (1925) 
published a picture of this building, and with his kind assist- 
ance I had it rephotographed in 1926. (See Plate II.’) But 
in February, 1929, Mr Bouricius unfortunately died: and 
later in the same year, when Dr Schierbeek was about to 
propose to a Dutch scientific gathering’ that a commemora- 
tive tablet should be placed on the house, he found that it 
had just been pulled down—to enlarge the playground of 
another children’s school ! 

It will thus be seen that the house in which Leeuwenhoek 
was born, the other house in which he lived and worked 
and traded and died, and even the house in which he is 
now erroneously supposed to have resided, have all been 
demolished. Delft, Holland, England, London, the Royal 
Society, and everyone else in every land, may therefore all be 
censured for having done nothing to preserve Leeuwenhoek’s 
bodily connexion with the world. 

But it is needless to bewail the hard fact that such 
material relics of Leeuwenhoek’s existence have been thus 
wantonly destroyed. His own works are a monumentum aere 
perennius which no vandal or house-breaker or Fellow of the 
Royal Society can ever annihilate. For my own part, I feel 
no sorrow when I reflect that the site of his own dwelling 
is now occupied by an obscure modern shop: and I almost 
rejoice that the place where he was born, and the ground 

1 This photograph has already been published, unfortunately, by Dr 
Schierbeek (1930), though it was taken at my expense for the present work. 
I note this lest I be accused of borrowing his illustration without 

2 Genootschap voor Geschiedenis der Genees-, Natuur- en Wiskunde. 



whereon he is wrongly supposed to have lived, are both now 
open spaces where little Dutch children can play in the sun. 
I even find something appropriate, poetic, and comforting in 
these ‘‘ inscrutable dispensations of Providence.” 


It is well known that most of the illustrations accompanying 
Leeuwenhoek’s letters were not drawn by his own hand. He 
tells us himself that he was a poor draughtsman, and therefore 
employed more skilful artists to make his figures.’ There are 
several references to this subject in his published works ; but 
perhaps the most explicit expression is to be found in an early 
unpublished letter, wherein he says—in answer to Oldenburg’s 
complaint that his drawings were not sufficiently clear—that 
he sees with the utmost clarity all that he describes, but then 
adds :° 

Yet I am to blame, because I can’t draw; and secondly, 
because I am resolved not to let anybody know the 
method that I use* for this purpose: and so I just make 
only rough and simple sketches with lines, mostly in 
order to assist my memory, so that when I see them I 
get a general idea of the shapes: besides, some of the 
forms I see are so fine and small, that I don’t know how 
even a good draughtsman could trace them, unless he 
made them bigger. 

Many of the original drawings sent with the letters to the 
Royal Society have been preserved. They are, for the most 
part, of no great artistic merit, and differ in minor details 
from the published engravings. This is, in the main, because 
the originals were usually drawn with red or black chalk, or 
pencil (exceptionally with ink or in colour), and were often 
reduced in size by the engraver. All variations are readily 
explicable by the difference in technique—the soft line made 
with red crayon on paper being impossible to render exactly 
by the hard line of the burin on metal. On the whole, the 

1 Cf. Letter 2, p. 42 supra. 
2 Translated from Letter 11. 26 March 1675. To Oldenburg. MS.Roy.Soc. 
* je, in handling the microscope—as is evident from the context. 


engravers dealt faithfully with their prototypes: and I 
fancy that the average modern editor, if drawings such as 
Leeuwenhoek’s originals were submitted to him in illustration 
of a present-day paper, would return them to the author with 
a note saying that they were “not suitable for reproduction”. 
I have, indeed, been compelled to act on this principle myself : 
the original drawings, en sanguine on discoloured and yellowish 
paper, illustrating the letters on Anthophysa and the protozoa 
on duckweed, are still extant; but I cannot reproduce them 
here—for technical reasons—and have had to use the 
engravings originally made from these drawings instead. 

A few “rough and simple sketches ’’—mostly on the mar- 
gins of the MSS.—were evidently the work of Leeuwenhoek 
himself’: because careful examination shows that they 
were drawn with the same pen and the same ink as the 
accompanying autograph handwriting. They bear out his 
own statement that he was no artist. 

In Leeuwenhoek’s letters I have been unable to find any 
mention of the name of the draughtsman—“‘de teijckenaer’’, or 
“the limner’”’ as Hoole always calls him—who made his 
illustrations for him. (He is frequently mentioned, but never 
by name.) It is unlikely, indeed, that all the drawings were 
executed by the same artist, for they were made at intervals 
during some 50 years; and there is no reason to believe that 
Leeuwenhoek’s longevity was characteristic of all citizens of 
Delft at that period. It seems to me certain, therefore, that 
more than one hand must have participated in the illustration 
of his discoveries. 

It is generally supposed that Leeuwenhoek’s draughtsmen 
are unknown. Nevertheless, there is at least one important 
record bearing on this subject which seems to have been 
overlooked. In Boitet’s book on Delft (1729; pp. 790-91) we 
are told of a certain Thomas van der Wilt (born 1659”), who 
was ‘‘a fine painter and a good poet,” and who was a pupil of 
Johannes Verkolje. It is said by Boitet that he settled in 
Delft, and there found plenty of work as a portrait-painter and 
otherwise; and “ By his wife Johanna Biddaff he had a son, 

1 The cube illustrating the argument in the letter to Const. Huygens 
(p. 189 supra) is one as these: and the pepper-tube (Plate XXII) is 

* He died at Delft in 1733 (fide Bryan, 1905). 


called Willem, who made such progress in drawing, through 
his father’s instruction, that there were few who could match 
him. Nearly all the plates in the celebrated work of Mr. 
Leeuwenhoek were marvellously drawn from life by him 
through magnifying-glasses. .... But hediedin the flower 
of his life on 24 January 1727, at the age of 35.” 

There is no reason to doubt the truth of this story— 
published only two years after Willem’s death in his home 
town: but it is impossible to believe that Willem van der Wilt 
drew “nearly all” (meest alle) Leeuwenhoek’s figures. If he 
died aged 35 in 1727, he must have been born in 1691 or 1692; 
and consequently he could have drawn none of the illustrations 
for the letters written in the XVII Century. He probably 
made the illustrations of the Send-brieven: but he could not 
have been responsible for any others—save some of those 
reproduced between 1700 and 1712 in the Phil. Trans. The 
pictures of vorticellids and rotifers published at the beginning 
of the XVIII Century may perhaps have been drawn by hin, 
and it may well have been Willem who made the recorded 
remark about their surprising “ wheelwork”’’.* But he must 
have been a mere child at the time. 

Whilst there is thus good reason to believe that 
Leeuwenhoek’s last letters were illustrated by Willem van 
der Wilt, there seems to be no direct evidence to show who 
drew the figures for the earlier ones. Nevertheless, it seems to 
me probable that some of them may have been drawn by his 
father Thomas. If we consider all the evidence furnished by 
Boitet, it appears to me highly suggestive. Very briefly, it is 
as follows: (1) Thomas van der Wilt was an artist living in 
Delft at the time when Leeuwenhoek wrote his early letters. 
(2) His son was employed by Leeuwenhoek to illustrate his 
later letters. (3) Thomas himself must therefore have been 
known to Leeuwenhoek.’ (4) He (Thomas) earned a good 
living in Delft not only by painting portraits, but also by 
exercising his artistic abilities in other ways. (5) Thomas’s 
father, though not a native of Delft, was a linen-draper—the 
trade which Leeuwenhoek himself engaged in. (6) Thomas 

* Cf. p. 279 supra. 

2 This is confirmed by the cireumstance—mentioned a little later—that 
Thomas was responsible for some panegyric verses elucidating the allegorical 
title-page of the Send-brieven. 


was a pupil of Verkolje—the artist who painted Leeuwenhoek’s 

What could be more likely, therefore, than that 
Leeuwenhoek employed Thomas van der Wilt to draw the 
pictures for some of his earlier epistles? When all the 
circumstances are taken into account, this seems to me to 
be something more than a plausible guess at the identity of 
one of the original draughtsmen. 

But Leeuwenhoek must have known other artists who 
lived in his native town, and the evidence in favour of Thomas 
van der Wilt is clearly not conclusive. Among Leeuwenhoek’s 
acquaintances we must include, for example, that incomparable 
painter Jan Vermeer. He was born in the same year as 
Leeuwenhoek, in the same place, and at almost the same 
hour (their baptisms are registered on the same page), and 
lived and worked all his life in Delft—of which he has left us 
one of the most beautiful pictures in existence (see Plate VII). 
Moreover, we know that, on Vermeer’s untimely death in 
1675, Leeuwenhoek was appointed as his executor.’ 

I must note, in conclusion, that Thomas van der Wilt once 
painted a portrait of the poet Hubert Poot (1689-1733), who 
wrote Leeuwenhoek’s epitaph ; and an excellent engraving of 
this picture, by Houbraken, was prefixed to Poot’s collected 
Gedichten (Delft, 1722)—reproduced here in Plate XVI. 
I have seen no other specimens of Thomas’s artistic work, 
but according to Boitet and others he also painted the 
Rev. Mr Gribius—Leeuwenhoek’s minister, who announced 
his death to the Royal Society (see p. 93 supra). The only 
sample of Thomas's poetry which I have seen is the poem 
explaining the engraved title-page—‘ Op de Titel-prent’’— 
of Leeuwenhoek’s Send-brieven (1718: not printed in the 
Latin edition [Epist. Physiol.]|, 1719). 

For my part, I accept Boitet’s evidence that Leeuwenhoek’s 
later letters were illustrated by Willem van der Wilt, and 
I incline to the view that some, at least, of the earlier ones 
were illustrated by his father Thomas. But the subject 
obviously demands further research, which I must leave to 
future students possessed of the time and opportunities 
requisite for pursuing inquiries of this character. 

1 Vide p. 35 sq., supra. It is noteworthy also that L.’s microscopes 
were ultimately auctioned in the chamber belonging to the artists’ Guild of 
St. Luke—of which Vermeer was sometime “ Master ”’. 




Several “portraits of Leeuwenhoek” are still extant. 
They were made at various dates by various artists, and the 
following fragmentary notes upon them may be of interest— 
information on this subject being somewhat difficult to obtain, 
and not having been previously collected.’ 

(1) By JoHANNES VERKOLJE (1650-1693 : lived at Delft 
1673 till his death, and is buried there. Cf. v. Riemsdijk, 
1921, p. 281). There are two portraits of Leeuwenhoek by 
this artist : 

(a) An otl-painting. (See Plate XI, opposite p. 49 of 
the present work.) Dated 1686 (fide Moes, 1905). Three- 
quarter length, showing Leeuwenhoek seated at a table; 
wearing a golden-brown robe, a wig, a knotted white necker- 
chief, etc. Head turned to left of picture (7.e. to his own 
right), knees to right. On the table a globe, an ink-stand 
with a quill pen, the sealed diploma of the Royal Society, a 
small pair of compasses, and a sheet of paper bearing a 
drawing of acircle and some indistinct figures. (The drawing 
appears to be that here shown in text-fig. 38, p. 202.) In 
his right hand he holds another pair of compasses.” He 
is depicted with a fresh complexion and clear blue eyes. 
An opening at the right in the dark background shows 
a glimpse of a distant landscape with a winding river 
(“perhaps the Thames” according to Haaxman—but why 
not the Maas?). 

This painting was formerly in the possession of Dr C. H. W. 
van Kaathoven of Leyden (Haaxman, 1875, p. 177: Harting, 
1876, pp. 117-119). On his death it was purchased (19 June 
1879) by the Rijksmuseum, Amsterdam, where it now hangs 
(Room 273, No. 2521). Cf. Moes (1905, p. 12); v. Riemsdijk 
(1921, p. 281). This isthe prototype of most of the published 
portraits. It has been reproduced in recent times by 
Crommelin (1926), van Seters (1926), and others, while 

1 Since this was written a short article on the same subject has been 
published by de Lint (1931)—too late for its contents to be discussed here. 

2 A little passer similar to this, and once belonging to L., is still (or was 
in 1923, when I saw it) in the possession of Mr P. A. Haaxman at The 


Haaxman had it lithographed'—by A. J. Wendel, not very 
successfully—as a frontispiece for his biography (1875). 

(b) A mezzotint engraving. (See the Frontispiece.) This 
differs from the painting chiefly in the following particulars: 
the head is turned to the right, knees to the left; and 
Leeuwenhoek holds a microscope in his left hand (not com- 
passes in his right). The whole picture is, in fact, reversed. 
On the table, instead of the diploma, there is a spray of oak- 
leaves with galls” on them, and a large magnifying-glass 
with a handle. A curtain hangs behind the head, and the 
distant landscape is missing. Below is engraved a Dutch 
inscription with some verses signed “‘ Constanter ” (the pen- 
name of Constantijn Huygens pater). The mezzotint is 
signed “J. Verkolje pina. fec. et exc. A°. 1686.”* (This is 
important, as it confirms the date of the painting.) 

Several prints, at least, of this engraving are in existence. 
Dr van Kaathoven, of Leyden, formerly possessed one, which 
afterwards passed into the possession of Mr P. M. Beelaerts, 
who in turn bequeathed it to the town of Delft." (It is now 
in the Gemeentemusewm.) But the best impression which I 
have seen is in the private collection of Mr George H. Gabb 
(London), from whose copy my frontispiece has been repro- 
duced. Other reproductions of the mezzotint (from other 
originals) have previously been published in Opuscula Selecta 
Neerlandicorum, Vol. I (1907); by Locy (1910, p. 79) and 
Cole (1926, frontispiece); and in the Deutsche Medizinische 
Wochenschrift (1911; No. 22, supplement). This last plate— 
included in that journal’s ‘‘ Bildersammlung aus der Geschichte 
der Medizin’’—is a fine large half-tone reproduction, but bears 

1 This poor lithograph has unfortunately been copied (instead of the 
equally accessible original) by several well-meaning popular writers—such 
as Baumann (1915) in Holland, and Mrs Williams-Ellis (1929) in England. 

2 Letter 50, 14 May 1686 (published in Dutch and Latin works) contains 
a description of L.’s observations on oak-galls, and its date affords confirmation 
of the date of the engraving. 

3 Not 1685, as stated by Haaxman (1875, p. 187). 

4 Of. Haaxman (1875) and Veldman (1898, p. 74). I have seen this 
impression, which is fairly good. 

* I am greatly indebted to Mr Gabb for his permission to copy the 
original in his collection, and for the trouble which he has taken to insure 
its accurate photographic reproduction. 


a ridiculous biographical note (signed ‘“‘ Pagel’’) on its back. 
The original picture is therein hesitatingly attributed to 
“J. Veikolpe”’, and “Anton” van Leeuwenhoek is called a 
‘well-known precursor of Robert Koch, in so far as the 
discovery of the infusoria is due to him.” 

It seems obvious that Verkolje first made his portrait of 
Leeuwenhoek in oils, and shortly afterwards (in the same 
year) himself engraved it in mezzotinto. The artist evidently 
copied his own painting directly on to the copper plate (which 
accounts for the figure being reversed in the printed engraving), 
and in doing so made several minor alterations or improve- 
ments—appropriately substituting a microscope for the 
compasses originally held in the hand, but failing to notice 
that he ultimately made Leeuwenhoek appear left-handed ! 
The mezzotint by Verkolje is probably the best of all portraits 
of Leeuwenhoek: and that it was an excellent likeness is 
attested by the verses written on it by Const. Huygens. 

There are several references to this mezzotint by 
Leeuwenhoek himself in unpublished passages in his letters. 
Apparently the Royal Society wrote, about the beginning of 
1694, to ask him for his portrait. In his reply he says: ’ 

I haven't any of my pictures; and furthermore, the 
plate has been printed off, and the plate-maker, who was 
also the printer and painter,” is dead. But if I can get 
one at our approaching annual fair, at which time many 
art-dealers come to our town, I’ll not neglect to let you 
have what you ask for. 

Later in the same year he wrote again: ° 

I couldn’t find any copies of my portrait, in mezzotinto,* 

for sale by any of the printsellers at our annual fair: but 
at last ’'ve gotten six copies from a bookseller in another 

1 Translated from Letter of 26 May 1694. To R. Waller. MS.Roy.Soc. 

2 Referring to Verkolje, who died in the previous year. 

3 From Letter 84. 14 September 1694. To R. Waller. MS.Roy.Soe. 
Published in Dutch and Latin printed works, but with the passage here 
translated entirely omitted. Not in Phil. Trans. 

* inde swarte konst MS. 


town, which I dispatched a fortnight ago to London by 
Skipper Richart Houlatson, with the address: For the 
Secretary of the Royall Society at Gresham Colledge, 
without any further inscription. 

The Royal Society failed to acknowledge the receipt of 
these letters and pictures (and also of other letters from 
Leeuwenhoek received at that time), and two years later we 
find him writing again *: 

When I learnt that several Fellows were wishful to 
have two or three copies of my portrait, printed in 
mezzotinto, . . . I couldn't remain idle, but made 
every effort to satisfy them; and finally I obtained six 
prints (as the plate had been printed off). These mezzo- 
tintos, as also my Latin book, I sent to London, and 
addressed them, as I’ve been wont to do, to Gresham 
Colledge: to all which letters I got no answer 

What happened to these six prints is not now known. 
They have all disappeared from the Royal Society’s collection, 
and the Society now possesses only a single mutilated copy of 
the mezzotint acquired at a much later date. 

All the well-known engraved portraits of Leeuwenhoek are 
derived from Verkolje’s oil-painting. The best-known, and 
most often reproduced, is the excellent copperplate engraving 
by A. de Blois prefixed to the Dutch and Latin collective 
works (Brieven and Opera Omnia). It first appeared as a 
frontispiece to the Vervolg der Brieven (1687), with a Dutch 
inscription: afterwards, with Latin lettering, in Arcana 
Naturae Detecta (1695). Various copies of this copy have 
also been made—in line, stipple, mezzotint, and by modern 
photographic processes. At least one early engraving was 

1 The words “For . . . Colledge” are thus in English in the MS. 
(The rest, of course, is in Dutch.) 

2 From Letter 102. 10 July 1696. To the Royal Society. MS.Roy.Soc. 
Published—with omission of the passage here translated—in the Dutch 
and Latin printed works: English extract in Phil. Trans. (1696), Vol. XIX, 
No. 221, p. 269 (from which the passage isalso absent). This letter actually 
contains a protest against the Society's failure to acknowledge 8 of L.’s 
communications (Letters 77 to 84)—a discourtesy which caused him to 
start sending his observations to other people instead. 


reproduced in colours. The best steel-engraving (copied from 
de Blois) is that by A. Smith,’ prefixed to Hoole’s Select 
Works (Vol. I, 1798): but another good one—probably copied 
from Smith’s, but with the head turned to the right (as in the 
original mezzotint)—was made by J. Chapman and published 
by G. Jones in 1813. All these reproductions show 
Leeuwenhoek’s head only, in an oval frame with more or 
less added decoration. 

Regarding Anker Smith’s engraving (in Hoole) the 
following points should be noted. Although it bears an 
extract from a Dutch letter printed in 1696, and is marked 
“ Painted by I. Verkole”’, it was almost certainly copied from 
the engraving by de Blois accompanying the Latin Arc. Nat. 
Det. The oval frame bears the words: “ANTONIUS A 
MDCXCV.” Both age and year are entirely wrong, and 
consequently this circumscription has already led to mis- 
understanding. JI can only suppose that Smith (or Hoole) 
wrongly took the date of the Arc. Nat. Det. (1695) as that in 
which de Blois’s engraving was made; and that the age of 63 
was then inferred from this error. Anyway, there can be no 
doubt that Smith’s engraving was ultimately derived from an 
original made in 1686 (not 1695), which portrayed 
Leeuwenhoek at the age of about 54 (not 63). 

Verkolje’s portraits have been copied and recopied over 
and over again, and terribly travestied and perverted in the 
process. ‘The die of Leeuwenhoek’s own seal * was admirably 
incised from the mezzotint: the modern bronze effigy’ of 
himself, now suspended in Oude Delft, is also based—less 
successfully—on Verkolje’s originals. Moreover, there are 
contemporary tiles and pottery of Delft-ware bearing 
Leeuwenhoek’s supposed simulacrum “ after Verkolje” (a very 
long way after). I have seen two samples of these—a plate 
and a plaque—now in the Riyksmuseum; and Haaxman and 
Harting mention others. I have also seen a present-day 
descendant of Verkolje’s pictures—showing “the man who 

1 Anker Smith (1759-1819), a once celebrated engraver of small plates 
for book-illustration. He was elected.A.R.A. in 1797. 

2 Ct. p:. 360. 
3 Cf. p. 340 supra. 


first saw a microbe”—in an English children’s magazine, 
and a comic reconstruction recently (1931) used to advertise 
an American proprietary tooth-paste in India: but the last 
stage in degradation has surely been reached in the caricature 
imprinted on the covers of the current American Abstracts of 
Bacteriology (Vol. I issued in 1917) and some other publications 
of the Society of American Bacteriologists. 

(2) By Nicotars Mass (1632-1693: from 1673 to 1693 
at Amsterdam, where he died and was buried). According 
to C. H. de Groot (1916: Vol. VI, pp. 530-531) there are 
two portraits of Leeuwenhoek by Maes. The first (No. 202, 
de G.) is an oil-painting now in the National Gallery, London 
(1921 Catalogue, No. 2581). This picture was formerly owned 
by Mr George Salting, the Australian art-collector, and was 
bequeathed to the Nation in 1910. It is undated, and depicts 
an old man “in full face. His right hand is raised, grasping 
his robe. He has long hair, a moustache, and a pointed beard 
on his wrinkled face. |He wears a black robe and a white 
shirt.| At the back is a curtain, with a column in shadow to 
the right’ (de Groot). This is a very fine painting, but it is 
certainly no portrait of Leeuwenhoek. It shows a man totally 
unlike the sitter for Verkolje’s portraits, and there is no 
evidence whatsoever that it depicts our Antony. In 1923 
I called the attention of the then Director of the National 
Gallery (Sir Charles Holmes) to this misidentification: and on 
looking into the matter for himself he agreed that ‘‘ there is 
no just ground for identifying the portrait . . . as a portrait 
of Leeuwenhoek.” He informed me further that the picture 
was first labelled “ Anthony van Leeuwenhoek, F.R.S.” after 
it left the Salting Collection—by whose authority is not now 
known.” Its label has consequently now been changed to 
“ Portrait of a Gentleman”. De Groot blundered badly when 
he accepted this painting as a portrait of Leeuwenhoek. 

According to de Groot there is also another portrait (like- 
wise undated) by Maes. It is described as follows: ‘‘ 202a. 
ANTHONI VAN LEEUWENHOEK.—In a dark red coat trimmed 
with fur. His long hair falls on his shoulders. 28 inches by 
24 inches. Sale.—Lady Anna Chandos-Pole and others, 

1 See Anonymus (1927). 
2 Letters dated 8 & 10 May 1923. 


London, July 19, 1914. No. 106” (de Groot, 1916: Vol. VI, 
p.531). Whether this is a genuine portrait or not I do not 
know. I have been unable to trace it further. I can only 
add that according to Art Prices Current, 1913-1914 (Vol. VI, 
pp. 307, 505), the picture was not the property of Lady Chandos- 
Pole, but belonged to Maj.-Gen. Sterling, of 249 Knightsbridge, 
London, and was sold at Sotheby’s on 29 April 1914 for £46: 
while later in the same year (10 July 1914—not 19 July, as 
stated by de Groot) it is said* to have been resold at Christie’s 
for £120. 15s. 

Notwithstanding the allegations of de Groot and others, 
there seems to be still no satisfactory evidence to prove that 
any portrait of Leeuwenhoek was ever painted by Maes: but 
the matter obviously needs further investigation. 

(3) By ADRIAEN VAN OsTADE (1610-1685: born at Haarlem, 
where he worked and died). See Moes (1905; Vol. IT, p. 12) 
No. 4415 (1): de Groot (1910; Vol. IIT, p. 410) No. 876.—De 
Groot calls this a “ Portrait of Anthonie van Leewwenhoek (1632- 
1722), physicist and surgeon of Haarlem”’,” and he describes 
the picture thus: “ He sits, turned three-quarters left, and 
leans his left arm on the table and his right hand on his hip. 
He wears a black costume with a white collar and brown 
gloves. In front of him are a book and a celestial globe. 
Signed in full at the foot of the globe, and dated 1665; panel, 
81 inches by 7 inches.” This portrait is stated to have been 
sold in Paris on 2 May 1865 (Sale H. de Kat, No. 63). Ihave 
been unable to find it. I may note, however, that what 
appears to be a copy in black chalk, by A. Delfos, is preserved 
in the Municipal Museum at Delft. It is a poor portrait (if it 
be one) and bears little resemblance to the authentic pictures 
of Leeuwenhoek, though the face recalls many of the peasants 
portrayed in Ostade’s other paintings. 

Adriaen van Ostade was no portrait-painter (and in my 
opinion a very poor artist): and at present I am not convinced 
that he ever attempted to paint a portrait of Leeuwenhoek— 
or, if he did, that it is now in existence. 

1 Tt is also there said to represent ‘“‘ Lieuvenhoch, the father of the 

2 There are 5 obvious errors in these dozen words. 


(4) By CoRNELIS DE MAN (1621-1706: born, worked, and 
died at Delft). According to Moes (1905; Vol. II, p.12) 
there is—or was—a portrait of Leeuwenhoek by this artist, 
dated 1681, in the “ Anatomie-Kamer te Delft.” When I 
visited the town in 1923 I was unfortunately unable to find it: 
and subsequent inquiries made through the late archivist 
(Mr Bouricius), and the late Prof. Beijerinck, have been 
equally fruitless. 

(5) By JAN VERMEER (1632-1675, of Delft). There is no 
authentic record of any portrait of Leeuwenhoek having ever 
been painted by this great master. Nevertheless, it has 
recently been stated by Lucas (1922, p.8) that Leeuwenhoek, 
“the inventor of the microscope,” was “ probably his model for 
the three or four scientific pictures”. (By “scientific pic- 
tures” Lucas means those paintings by Vermeer showing a 
“Geographer” or “ Astronomer” at work.) I have not seen 
the originals of any of these (nor had Lucas when he wrote), 
but I have studied good photographic reproductions of them 
all. ‘There are four, and they appear to me to portray as many 
different people. No two are alike, and none bears any 
recognizable likeness to Leeuwenhoek—as we know him from 
Verkolje’s authentic portraits. I am entirely at a loss to 
understand how anyone can seriously suggest that Vermeer’s 
‘“Geographers”’ and “ Astronomers” all represent the same 
person—and that person Leeuwenhoek. ‘The suggestion 
becomes still more perplexing when we find that Lucas (op. cit., 
p.20) also accepts as genuine the spurious “portrait” by 
Maes '—which in no way resembles any of the people depicted 
by Vermeer or Verkolje. 

I must call attention, however, to some curious points 
which came to my notice whilst seeking evidence (not given 
by him) for Lucas’s statements. The very fine painting by 
Vermeer known as “ The Geographer,” now in the Stddelsches 
Institut at Frankfort,’ shows a man poring over a map or 
chart, and with a pair of compasses in his right hand. Behind 
his head there is a globe, and some other maps are also in the 

1 See above, p. 351. 

* There is an excellent reproduction in colour in “Jan Vermeer of 
Delft’ (Portfolios of Great Masters), published by Halton & Truscott 
Smith, Ltd. London, 1925. 



picture—a couple loose on the floor, one framed on the wall. 
This is one of the few of Vermeer’s pictures which is signed 
and dated. The date, painted on the wall behind, is 
MDCLXVIIII (z.e., 1669—not 1668, as stated by more than 
one writer on Vermeer). Now this is the very year in which 
Leeuwenhoek was appointed surveyor." Moreover, the globe 
in the picture is apparently a celestial (not terrestrial) globe, 
and is very like that shown in both of Verkolje’s portraits. 
Leeuwenhoek must surely have possessed a similar one. In 
Verkolje’s oil-painting, furthermore, Leeuwenhoek is shown 
holding a pair of compasses in his right hand *—just like 
Vermeer’s “Geographer”. The framed map on the wall has 
only an artistic import: it has no “ scientific” significance, 
being simply a decoration—introduced into many of Vermeer’s 
other pictures which have no connexion with geography. 
There is no authority for calling this picture “The 
Geographer ’”’—a modern label. Suppose we call it “The 
Surveyor”? This title seems equally appropriate; and we 
might then suppose that Vermeer was inspired to paint it by 
seeing Leeuwenhoek at work on ground-plans and surveys in 
preparation for his qualifying examination in 1669! But all 
this is mere guesswork, though the coincidences Just noted are 
curious—if nothing more. “The Geographer” himself is not 
much like Leeuwenhoek; and there is no evidence, as I have 
already remarked, that Vermeer ever painted his portrait. 

(6) By JAN GOEREE (1670-1731: designer, engraver, and 
poet. Known also as Gouré).—In the engraved title-page of 
Leeuwenhoek’s last published letters (Send-brieven and Epist. 
Physiol.) there is inset a little oval portrait circumscribed 
MDCXXXII”’. It is supported by a fat female angel blowing 
a trumpet, and somewhat overclouded by other allegorical 
accessories. The first state of this plate (in the Dutch 
edition) is lettered at foot “Te DELFT by ADRIAAN 
BEMAN, 1718.” and in the left bottom corner “J. Goeree 
sculpt: Direa.” The second state (Latin edition) bears the 
words “DELPHIS apud ADRIANUM BEMAN, 1719.” 
—with the same signature. 

1 Cf. p. 34 supra. 
* See Plate XI, facing p. 49. 


I formerly attached but little importance to this small 
detail—believing it to be on a level with the rest of the 
engraved title. Buta few years ago Dr W. H. van Seters, of 
Leyden, when collecting material for the ‘‘ Leeuwenhoek 
Film ” (which has now been exhibited on various occasions : 
cf. Kaiser, 1924), rediscovered’ an old design above which 
Leeuwenhoek once wrote a motto and his name. Dr van 
Seters kindly sent me a photograph of this drawing (included 
in the film), which reveals several points of interest. 
Leeuwenhock’s signature (undoubtedly genuine) is there dated 
30 April 1698. It is written at the top of the page, and is 
followed by a large allegorical drawing illustrating his motto f 
(“ Door Arbeyt en Naarstigheijt””). But this drawing was 
evidently added later, as it is signed “ J. Goeree del: 1707.” 
Moreover, it bears, as a pendant, the miniature portrait of 
Leeuwenhoek incorporated later in the engraved titles of his 
last letters. This picture was therefore probably made in 
1707—not at the date of publication of the Send-brieven 
(1718). Careful study of the engraving has also convinced 
me that it was made with considerable care, and under 
Goeree’s own supervision—as the words “sculpt: Durex.” 
sndicate. 1 therefore now regard this portrait (shown in my 
Plate XII) as a genuine and conscientious attempt, by fairly 
competent artists, to delineate Leeuwenhoek as he appeared 
in his 75th year. In any case, this is the only known portrait 
of him in his later life which can make any pretence to 


In conclusion, I must mention three slyptic representa- 
tions of Leeuwenhoek. The first is the profile portrait on 
the silver medal awarded to him in 1716 by the University 
of Louvain (see p. 80). This has already been depicted by 
van Loon and Haaxman. The medal is now in the Gemeente- 
museum at Delft; and as it was struck during his lifetime, its 

fA ee 

1 Tt was exhibited at the Leeuwenhoek Celebration in 1875, and was 
described by Harting (1876, p. 120). I think the picture was very probably 
intended as a title-page for the projected edition of L.’s letters (following 
No. 146 and preceding the Send-brieven) which was never published in 
Dutch or Latin.—According to de Lint (1931) the original is now in the 
collection of Dr J. van der Hoeven at Eefde [near Zutphen]. It is 
reproduced in Opusc. Select. Neerland., Vol. IX, Pl. III (1931). 

2 Given in full on p. 299 supra. 



maker may well have had Leeuwenhoek himself as a model. 
The portrait is therefore worth consideration. The second 
carved likeness is the white marble medallion on his tomb (see 
p. 100, and Plate XV). This was made after his death, and 
was probably modelled on the silver medal. It has less interest, 
therefore, as a portrait. The third representation is that on 
the “ Leeuwenhoek Medal,” awarded every ten years by the 
Royal Academy of Sciences of Amsterdam to persons who have 
distinguished themselves as microbiologists.' This medal is of 
gold, valued at f.300 (about £25), and has been described and 
figured by Harting (1876). The portrait which it bears is, 
however, a modern fake; and its historico-iconographical 
value is consequently mil. 


As Leeuwenhoek’s own collective editions of his works— 
both Dutch and Latin—begin with a letter called “No. 28”, 
dated 25 April 1679, it has generally been assumed that all his 
earlier letters (No. 1—No..27) have been lost. But this is not 
so: most of them have been preserved among the Royal 
Society MSS., and many have been printed in English or Latin 
(generally abbreviated) in the early volumes of the Philosophical 

I have discussed these letters in some detail in an article 
about to appear in Opuscula Selecta Neerlandicorum, Vol. IX, 
so I need not repeat what I have there said.” But as my 
numeration differs entirely from that of Vandevelde—who 
previously attempted to arrange and number them without 
consulting the original manuscripts—and as I have made 
frequent references to these letters in the foregoing pages, I 
give here a tabular synopsis for the reader’s convenience and 

1 The first award was made to C. G. Ehrenberg in 1875. The later 
recipients have been Ferdinand Cohn (1885), Louis Pasteur (1895), 
M. W. Beijerinck (1905), David Bruce (1915), and F. d’Herelle (1925). 

2 Since these lines were written, the article has appeared in print: see 
Dobell (1931). 





Addressed to Date Roy. Soc. MS. Published in Phil. Trans. 
H. Oldenburg ? [No MS.] | Vol. VIII, No. 94, pp. 6037-6038. 
[Transmitted 1673. [Extracts, in English. ] 
by de Graaf | Vol. VIII, No. 97, pp. 6116-6118. 
28 Apr. 1673] 1673. (Figures, with description in 
English. ] 

H. Oldenburg | 15 Aug. 1673 | L.1. 1 | Vol. IX, No. 102, pp. 21-23 and 
23-25 [in 2 parts]. 1674. [Extracts, 
in English.] 

H. Oldenburg! 7 Apr. 1674 | L.1. 2 | Vol. IX, No. 102, pp. 23-25. 1674. 
[Combined with part of Letter 2, 

| Extracts only, in English. ] 

H. Oldenburg | 16 Apr. 1674 | L.1. 83 | Unpublished 

Lys Ee Sa ee eee Lia Ala Pa Ne 

H. Oldenburg | 1 June 1674 | L.l. 4 | Vol. IX, No. 106, pp. 121-128. 1674. 
[Part only—in English. ] 

H. Oldenburg | 6 July 1674| L.1. 5 | Vol. IX, No. 106, pp. 128-131. 4674. 

| [Extracts only—in English. ]} 

H. Oldenburg | 7 Sept.1674 | L.l. 7 Vol. IX, No. 108, pp. 178-182 [mis- 
printed 821]. 1674. [Incomplete 
English translation. ] 

H. Oldenburg | 7 Sept.1674 | L.1l. 6 Unpublished 

H. Oldenburg | 19 Oct. 1674 | L.1. 8 | Unpublished 

H. Oldenburg | 4 Dec. 1674 L.1. 9 | Vol. X, No. 117, pp. 378-380. 1675. 
[Extracts in English. ] 

H. Oldenburg | 22 Jan. 1675 | L.1. 10 | Unpublished 

H. Oldenburg | 11 Feb. 1675 | L.1. 11 | Unpublished 

H. Oldenburg | 26 Mar. 1675 | L.1. 13 Unpublished 

H. Oldenburg | 14 Aug. 1675 | L.l. 15 Vol. X, No. 117, pp. 380-385. 1675. 
(Extracts, in English.] 

H. Oldenburg ; 20 Dec. 1675 | L.1. 16 Unpublished 

H. Oldenburg | 22 Jan. 1676 | L1. 16a | Unpublished 

H. Oldenburg | 22 Feb. 1676 | L.1. 17 Unpublished 

H. Oldenburg | 21 Apr. 1676} L.1. 18 Vol. XI, No. 127, pp. 653-656. 1676. 
[Incomplete English translation, 
with notes (by Nehemiah Grew).] 

H. Oldenburg | 29 May 1676} L.1. 20 Unpublished 

R. Boyle 28 July 1676 |[ With Unpublished 

Boyle MSS.] 
H, Oldenburg | 9 Oct. 1676 | L.1. 22 Vol. XII, No. 133, pp. 821-831. 1677. 

[Incomplete English translation. } 










Addressed to 

H. Oldenburg 




R. Hooke 

N. Grew 

N. Grew 

N. Grew 
N. Grew 

H. Oldenburg 

H. Oldenburg 

H. Oldenburg 


30 Oct. 
23 Mar. 

14 May 

5 Oct. 

16 Oct. 

.. Nov. 

14 Jan. 

18 Mar. 

31 May 

27 Sept. 
21 Feb. 










Roy. Soc. MS. 

L.1. 24 
L.1. 25 

ly 2 

ed; 29 

L.1. 32 

[No MS.] 

L.1. 33 

Lil. 34 

L.1. 36 

Ll. 88 
[No MS.] 

Published in Phil. Trans. 


Vol. XII, No. 134, pp. 844-846. 1677. 

{Incomplete English translation. ] 

Vol. XII, No. 136, pp. 899-905. 1677. 

[English translation. A full Latin 
translation of this letter was pub- 
lished later in Derham’s Philos. 
Ezpts. & Obss. of R. Hooke (1726), 
pp. 65-74. ] 

(Not in Phil. Trans. English ex- 

tracts published in R. Hooke’s Lect. 
& Collect, (1678), Part II, Letter 1, 
pp. 81-83: reprinted in his Lect. 
Cutlervanae (1679).] 


Vol. XII, No. 142, pp. 1040-1043. 

1679. [Full letter, in Latin. ] 

[Not in Phil. Trans. English ex- 

tracts published in Hooke’s Lect. € 
Collect. (1678), Part II, Letter 2, 
pp. 84-89: reprinted in his Lect. 
Cutlervanae (1679). ] 

Vol. XII, No. 142, p. 1044. 1679. 

(Abstract, in Latin. } 

Vol. XII, No. 140, pp. 1002-1005. 

1678. [Two extracts, in English.] 
Vol. XII, No. 142, p. 1045. 1679. 
[Latin summary of another part of 
letter. ] 


Unpublished [This letter is men- 

tioned by L. in his letters dated 
13 June 1679 (No. 28a, unpublished), 
13 Oct. 1679 (No. 280, unpublished), 
and 25 Apr. 1679 (No. 28— published 
in Dutch and Latin printed works). 
It was apparently lost in trans- 

mission. ] 

Addendum.—All the Letters marked ‘‘ Unpublished” in the foregoing 
list have now (with the exception of the last, which still remains lost) been 
printed in full in Vol. IX of Opuscula Selecta Neerlandicorwm, Amsterdam, 
This volume has appeared too late for its contents to be considered 
in the present work. 



In addition to the information given in this table, I must 
note the following points: 

(1) Leeuwenhoek sent a complete copy of his Letter 4 
(1 June 1674, to Oldenburg) to Const. Huygens, and the MS. 
is preserved at Leyden. ‘This copy has recently been printed 
by Vandevelde and van Seters (1925). 

(2) Letter 19 (23 March 1677) and Letter 21 (5 Oct. 1677) 
are quoted extensively by Leeuwenhoek himself, in his own 
language, in his Letter 96 (9 Nov. 1695, to the Elector Palatine) 
printed in the Dutch works—with Latin versions, of course, 
in the corresponding Latin editions. 

(3) Letter 22 (Nov. 1677) is quoted, almost entire, in its 
original Dutch, by Leeuwenhoek in his Letter 113 (17 Dec. 
1698, to Harmen van Zoelen—published in the collective 
editions) : and a complete English translation of it (made but 
not published by myself) has now appeared in the recent 
work of Cole (1930). 

(4) Finally, I must note that the printed Catalogue of the 
Royal Society MSS., compiled many years ago by the youthful 
Halliwell-Phillipps (1840), is not free from errors; and 
accordingly its entries relating to the Leeuwenhoek MSS. are 
not to be accepted as invariably accurate. 


Seals on old manuscripts are often important for purposes 
of identification: how important they may sometimes be, I 
know from the following incident. Recently, Carbone (1930) 
believed that he had discovered a new Leeuwenhoek letter 
among the Magliabecht MSS. in the National Library at 
Florence. This document was among the genuine letters of 
Leeuwenhoek addressed to the Florentine scholar, but was 
unsigned. Carbone reproduced it in facsimile—including the 
seal (enlarged). From its contents it was at once evident 
to me that this letter (written in Latin, and dated 2 May 1692 
from Hanover) could not possibly have been written by 
Leeuwenhoek. I guessed immediately, however, that it was 
written by Leibniz: and on comparing it with Leibniz’s 
extant letters to the Royal Society, I found that the cor- 
rections throughout were apparently made in his handwriting, 
and that the seal was one which he used. A seal is often 
as good as a signature (for no man lent his seal-ring to 


others), and I therefore felt satisfied that the letter was written 
by Leibniz and not by Leeuwenhoek. This I was soon able to 
confirm by discovering that the manuscript in question had 
actually been published previously as a genuine Leibniz letter 
by Targioni-Tozzetti (1746, pp. 119-122). 

Leeuwenhoek’s own seals have never yet been described. 
At various periods of his life he sealed his letters with at least 
three different ones—usually of red wax, but occasionally of 
black. Most of the extant impressions are imperfect—the 
seals having generally been broken, of course, in opening the 
letters. The following notes are put together from the avail- 
able fragments. They may assist future students in identifying 
his writings, but are as incomplete and imperfect as their 
originals. : 

(1) Most of the early epistles are sealed with the monogram 
shown in Plate XXXII (upper figure). This is taken from an 
almost perfect impression on Letter 3a (16 April 1674)— 
stamped from an oval die measuring approximately 16 mm. by 
14mm. The letters APL presumably stand for A[ntony] 
P[hilipszoon| L[eeuwenhoek] ; the rest of the device I cannot 
interpret with any confidence. Above, there appears to be an 
arabic numeral 4: below, connected by a vertical line, the 
roman figure xx or (more probably) xxv can be read. 

(2) Another early seal—which I am unable to reproduce— 
was a heraldic device, all extant impressions of which are 
more or less fractured or indistinct. The die was apparently 
oval, about 17 mm. by 16 mm., with a slightly beaded border. 
The available examples show a small shield, bearing four 
raised vertical lines, surmounted by a helmet. On the field 
behind are various irregularly distributed plumules (?), but no 
lettering or other recognizable figures. This seal is affixed to 
several early signed and authentic letters to the Royal Society 
(including No. 13, 20 December 1675, from which an extract 
is here translated). The armorial bearings I have been unable 
to identify. I can only add that an identical scutcheon with 
four vertical lines is several times figured by Boitet (1729) as 
the coat-of-arms of the Uttenbroek family—a family with 
which Leeuwenhoek is not known to have been connected. 

(3) Nearly all the later letters, when sealed, bear a portrait 
of Leeuwenhoek himself. The die used for this seal (see 
Plate XXXII, lower figure) was evidently cut with very great 
care and precision, and the various impressions—in red (rarely 

facing p. 




For description see the text. 


a 2 

r us eur ge hr aa yr 
re eh » a ako oat 0 ee 


in black) wax—show an astonishing amount of detail when 
closely studied. The seal was obviously copied from Verkolje’s 
mezzotint portrait of Leeuwenhoek (1686): it shows his 
bewigged head, as there depicted, with a curtain behind, and 
even reproduces such minutiae as his little moustache. Most 
impressions, however, are faulty or badly fractured. The best 
(from which my figure here is reproduced) is on Maria’s letter 
to the Royal Society." I judge the original die to have 
measured—outside its beaded border—approximately 21 mm. 
by 18mm. But I cannot be sure, as most impressions are so 
imperfect. (The specimen figured by Carbone (1930) is 
extremely poor.) 

This seal cannot have been used by Leeuwenhoek before 
1686, when Verkolje made his mezzotint. It may therefore 
possibly help to date some of his undated letters in future. 
The artist who cut the die is not known; but he must have 
been extremely skilful, for his work reveals—on careful study 
of good impressions—a degree of accuracy in reproducing 
minute detail which is really remarkable. Unfortunately, the 
dies of all the seals are now lost. 


1 See p. 98 supra. There are two seals on this letter, but only one is 
perfect. The other is distorted by a slip in impressing the wax. 



Protozoology and Bacteriology ”’, and I now repeat this 

title—which has since been adopted by others—on the 
title-page of the present work. I do this designedly, because 
in my opinion he alone deserves this designation. In my 
opinion (which has not been formed too hastily) he was the 
first man who ever saw living protozoa and bacteria under 
a lens, and by correctly interpreting and describing his obser- 
vations he created the modern disciplines of Protozoology and 
Bacteriology. Consequently, his relation to these sciences is 
that of “father” or “only begetter’”’. 

Nevertheless, there are still some people who dispute 
Leeuwenhoek’s claim to the discovery of the Protozoa and the ~ 
Bacteria, while there are others who bestow upon him titles 
which he does not deserve—as he himself would freely have 
confessed. He has already been styled “Father” and 
‘Founder ’”’ of Micrography by Blanchard (1868) and Vande- 
velde (1922)—to mention no other authors: though it is 
obvious that Pierre Borel and Henry Power and Robert Hooke 
and Marcello Malpighi have all at least as good a right to the 
title. Launois (1904) obviously goes rather too far when he 
calls Leeuwenhoek one of the “ Fathers of Biology’’: there is 
more evident justification for those who regard him as the 
“Father ” of Histology or Cytology or Haematology ‘"—or even 
as just the First Milk-Analyst.” Almost every writer who 
discusses Leeuwenhoek’s work regards him, apparently, as 
“father” of his own speciality—some strangely misinformed 
but enthusiastic authors even hailing him as “the Inventor 

A FEW years ago I called Leeuwenhoek “Father of 

1 Sabrazés (1926). 
2 Wynter Blyth (1903). 


of the Microscope”.’ Many such claims are manifestly 
absurd; yet his own right to be regarded as the Father of 
Protozoology and Bacteriology is, I believe, real and 

The discovery of the microscope is still in dispute, but I 
need not discuss the subject here. Its invention is intimately 
bound up with that of the telescope, and the rival claims of 
Italy and Holland in this connexion have been ably defended 
in recent times by Govi (1888), and Harting (1850) and de 
Waard (1906) respectively. The question has also been 
critically considered lately by Singer (1921) and Disney (1928). 
For present purposes it will suffice to note that one form of 
the microscope (¢.e., the compound microscope, to which the 
name is properly applied) was probably devised in Holland in 
the first decade of the XVII Century (not earlier), while 
immediately afterwards another form was independently 
discovered in Italy. But Leeuwenhoek probably knew nothing 
of all this, and it is unnecessary to argue here about the 
priority of Zacharias Janssen, Lipperhey, Drebbel, Galileo, or 
any other possible “inventor of the microscope”. Leeuwen- 
hoek did not use a microscope, but only a simple lens; so 
that the invention of the compound instrument (which 
occurred before he was born) has no bearing whatsoever upon 
his own work or discoveries. 

The discovery of simple lenses is, however, also a subject 
of dispute. It is now known, from the profound researches of 
the French scholar Martin (1871), that the ancients knew 
nothing about magnifying-glasses—notwithstanding the con- 
fident assertions of Dutens and many another more recent 
writer. Our Roger Bacon® (circa 1214-1294) had at least a 
glimmering of the properties and possibilities of lenses, but 
the first were probably made, and used as spectacles, about 

1 Byen since these lines were written I have read a paper (Chapman, 
1931) in which it is said that L.’s observations “ have earned for him the 
title of ‘The Father of Microscopy ’.” 

2 This excellent and fully documented work appears to have been over- 
looked by all recent writers on the history of the microscope—including 
Singer and Disney. 

3 Of. Bridges (1914). In this connexion the reader may also consult 
with profit the recent historical analyses by Singer (1921) and Disney e¢ al. 
(1928). The literature dealing with Bacon is too vast to cite here. 


the year 1300 in Italy—their popularization “for the help of 
poor blind old men” being chiefly due to the pious and 
private labours of the monk Alessandro de Spina of Pisa. 
The actual inventor of spectacles, however, is said to be a 
Florentine—Salvino d’Armato degl’Armati.’ Friar Bacon 
and his brethren in Italy were probably the originators of 
simple lenses; and the unknown people who first wore 
spectacles and used ordinary magnifying-glasses—for assis- 
tance in reading or for personal amusement—are the real 
“precursors ” of Leeuwenhoek as a “ microscopist ”’.” 

According to Govi (1888), the word “ microscope” 
(microscopio) was invented by Giovanni Fabri*—one of the 
earliest members of the Accademia dei Lincei—who first used 
it in a letter to Federigo Cesi dated 13 April 1625. The first 
pictures made with the aid of this instrument are usually 
supposed to be those of the bee and weevil interpolated by 
Francesco Stelluti (1630) in his Italian translation of the 
poems of Persius. The first “micrography ” is the Century 
of Microscopic Observations by Pierre Borel,* published in 
Latin at The Hague in 1656: but it was soon followed by the 
similar work of Henry Power’ (1663-4) and the more 
celebrated Micrographia of Robert Hooke (1665)—both 
written in English and printed in London. 

The writings of Stelluti and Borel and Power and Hooke 
all antedate anything that Leeuwenhoek ever published. 
But when he wrote his first letters he had probably never 
heard of any of these authors: and as he could read neither 
English nor Latin nor Italian, they could have afforded him 

1 Cf. Redi (1678), Mensert (1831), Harting (1850), Pansier (1901), etc. 

2 I cannot refrain from mentioning here a remarkable fantasy recently 
published by our greatest living English poet and novelist—an unhistorical 
story revealing more than superficial historical knowledge. I refer to 
Rudyard Kipling’s “The Eye of Allah”, printed in his volume entitled 
Debits and Credits (8° London, 1926). 

3 Fabri or Fabro, in Italian. His real patronymic was Faber, and he 
was descended from a family of this name who came from Bamberg in 
Bavaria. Cf. Carutti (1883, pp. 25, 39), ete. 

4 Pierre Borel, alias Petrus Borellus (1620-1689), a French physician, 
antiquary, and philologist. Cf. Nowv. Biogr. Gén., VI, 697. 

* Henry Power (1623-1668), M.D. Educated at Christ’s College, 
Cambridge, and practised as a doctor at Halifax. He was one of the first 
Fellows of the Royal Society—having been elected in 1663. 


little help—even had he seen their works. Moreover, there 
are no descriptions of protozoa or bacteria in any of these 
publications—so far as I have been able to ascertain. I have 
studied them all with care, but have sought information on 
such organisms in them in vain. I believe they contain none, 
and nobody (to my knowledge) has yet proved that they do. 
Nobody now claims that Fabri or Stelluti or Power or Hooke 
discovered the Protozoa or the Bacteria: but a half-hearted 
claim has recently been made for Borel by Singer (1915), so 
I cannot altogether ignore it here. 

Borel (1656) tells us that “worms” are said to be found in 
the blood of people suffering from “ fever”’,' though he makes no 
claim to have seen such things himself. Yet Singer says” that 
to him “It seems . . . highly probable that he caught a 
glimpse of infusoria and possibly bacteria, for he assures us that 
all decomposing material swarms with similar worms.” Singer 
gives no exact reference to the passage on which he relies, but 
apparently alludes to Borel’s Observatio de Sanguine ; in which 
he does not give any such assurance, but merely says it zs 
probable that worms would be found in every decomposing 
material if attention were paid to it.’ The whole passage is 
clearly hypothetical. As a prophecy it may have some interest 
for helminthologists: for the protozoologist or bacteriologist it 
is obviously without significance. Something more than a 
misreading or mistranslation of Borel’s words is surely needed 
to prove that he forestalled Leeuwenhoek. 

Another claim to priority in the discovery of the Bacteria 
has been put forward for the German Jesuit priest Athanasius 
Kircher (1602-1680)—well known as a voluminous and reckless 
writer on all manner of subjects.* I do not pretend to have 

1 Certo etiam refertur, in sanguine febricitantium vermes reperiri. 

2 Singer (1915), p. 338. Singer’s references to Borel are not always 
easy to follow. In two places, indeed, he appears to confuse Borel’s work 
of 1656 with his earlier publication of 1653. But this—so far as I can 
discover—contains only one trivial reference to the use of the “ engyscope”’ 
[= microscope], having no bearing on the present subject. Borel’s later 
observation (1656a, p. 198) on “ whale-like insects in human blood ’’—to 
which Singer also alludes—cannot conceivably refer to either protozoa or 

3 quare verisimile est idem in omni re, dum putrefit, contingere, si animad- 
vertatur (Borel, 1656; Obs. III, p. 8). 

4 Cf. Nouv. Biogr. Gén., XXVII, 769, and Allg. Dtsch. Biogr., XVI, 1. 


read all his works (which is probably impossible and would 
certainly be unprofitable), but only some parts of those which 
deal with biological topics. In none of them can I find any 
evidence whatsoever to indicate that he ever saw or described 
either a protozoon or a bacterium. But others believe that 
they have been more fortunate, so I must briefly consider their 

The first person to credit Kircher with the discovery of 
the Bacteria was, I believe, Friedrich Léffler (1887), who 
opens his work on the history of bacteriology with a quotation 
from the Scrutinium Pestis (1658)* wherein Kircher says: 
“That air, water, and earth are swarming with countless 
insects, is so certain that it can even be proved by ocular 
demonstration. It has hitherto also been known to everybody 
that worms swarm out of rotting bodies: but only after the 
wondrous invention of the Microscope did it become known 
that all decomposing things swarm with an innumerable 
brood of worms invisible to the naked eye: which even I 
myself would never have believed, had I not proved it by 
repeated experiment over many years.” * 

Now this passage contains no obvious reference to any 
organisms other than worms or insects—well known to 
everybody at the time when Kircher wrote: yet for reasons 
unexplained Léffler alleges that it “announces . . . the 
discovery of a new world of living creatures” —by which he 
means, presumably, the Bacteria. But does it? Surely not. 
The assumption is so far-fetched, indeed, that Léffler felt 
constrained to add that ‘“ Kircher was unable to give any 
more accurate data regarding these worms;” and he then 
made an irrelevant reference to the Ars Magna Lucis et 
Umbrae (1646). Any ordinary person would conclude that 
Kircher never described bacteria for the simple reason that 
he never saw them—and because Leeuwenhoek had not then 

1 Léffler actually quotes (in German translation) from an edition of 
1671, but gives no exact reference to the passage. I have not seen this 
edition, but it appears to be a reprint of the first Leipzig edition (1659), 
which I possess. In this the passage quoted (from Cap. VII, § II) is on 
p. 69. I have to thank Dr Singer for kindly lending me his own copy of 
the original edition of 1658. 

2 T translate from the original dog-latin of Kircher (1658)—not from 


published his discoveries. The organisms which Leeuwenhoek 
discovered were, for those times, of a ‘“Stupendious 
Smalness’’;* and there is good reason to believe that Kircher 
possessed no instruments capable of showing any objects of 
the order of magnitude of common bacteria. 

Singer (1914), however, has recently reasserted Léffler’s 
claims, and has attempted to support them with translated 
quotations from Kircher’s “ Experiments” with rotting flesh, 
leaves, and wood. ‘These are really too ridiculous to quote.” 
It is obvious—from Kircher’s own words—that he saw nothing 
but maggots, mites, and nematodes, such as anybody possessed 
of asimple low-power magnifying-glass can nowadays perceive. 
I have consulted all the passages on which Léoffler and Singer 
rely, and have repeated some of Kircher’s so-called experiments: 
and I have even read a considerable part of the Scrutiniwm 
Pestis and of the Ars Magna, and have made long search in 
Buonanni’s Micrographia Curiosa (1691) and Musaeum 
Kircherianum (1709). But the results have been incommen- 
surate with my labours. T'o me the Scrutiniwm Pestis appears 
as a farrago of nonsensical speculation by a man possessed of 
neither scientific acumen nor medical instinct.’ Kircher 
obviously had no conception of a real experiment—in the 
Baconian and modern sense. It is easy enough, of course, to 
tear a line here and there from his voluble writings, and to 
use it as evidence on his behalf: but if such lines be considered 
in their context they have a very different complexion. For 
instance, some recent authors have inferred that Kircher’s 
remarks about rats dying and decomposing at atime of plague 
show that he realized the relation of these rodents to plague- 

1 Grew (1701), p. 12. 

2 About ten years ago I had some correspondence with Dr Singer on 
this matter, and I then attempted to convince him of the error of his views. 
From his last letter to me on the subject I gather that he is no longer 
prepared to defend Kircher’s claim to the discovery of either the Bacteria or 
the Protozoa, and that he now accepts my interpretations. 

8 Kircher—who was a priest with no biological or medical training— 
had obviously derived most of his “ knowledge” from wide reading, and it 
seems to me not unlikely that in his vague references to ‘ worms”’ occurring 
in the blood of sick people he was merely harking back to the speculations 
of antiquity: for example, to the well-known passage where Pliny says 
“nascunturque in sanguine ipso hominis animalia exesura corpus ”’ 
(Hist. Nat., lib. XX VI, cap. xiii; ed. Genevae 1582, p. 488). 


epidemics. Iwish such authors would also explain, in modern 
terms, what Kircher meant when he recorded further how 
plague could arise likewise from a rotting mermaid. 

For my part, I cannot regard Kircher as anything more 
than the veriest dabbler in Science. His own writings 
appear to me unscientific in the highest degree, and I can find 
no evidence that he ever saw—even by chance—a protozoon 
or a bacterium through his “smicroscope.” His writings 
appear, consequently, to furnish no evidence whatsoever to 
prove that he forestalled Leeuwenhoek. But asI have already 
said, I have not read all his works. I can therefore only beg 
his supporters (if any there still be) to adduce some solid 
passage—which I have hitherto been unable to discover in his 
vast publications—to prove that he ever saw a protozoon. 
(Discussion of his “ discovery’ of the Bacteria may well be 
postponed until it has been demonstrated that he observed 
these larger organisms.) I am aware, of course, that Garrison * 
calls Kircher “the earliest of the microscopists”’ and says 
that he was “ undoubtedly the first to state in explicit terms 
the doctrine of a ‘contagium animatum’ as the cause of 
infectious diseases”’: but I submit that these statements also 
have not yet been substantiated, and I cannot conceive that 
they ever will be. Microscopists and contagiwm animatum 
both existed before Kircher began to write. 

This brings us to another line of argument against 
Leeuwenhoek’s originality—the argument from the doctrine of 
contagium vivum. It is as certain as anything historic ever 
can be that Kircher was not the first exponent of this idea: 
and there can be no doubt that the part played by “ animal- 
cules” in the causation of diseases was foreshadowed long 
before either Kircher or Leeuwenhoek was born.’ Some of the 
oldest known authors appear to have been familiar with the 

1 Garrison (1921), p. 250. 

2 In this connexion the paper by Singer (1913) should be mentioned, 
though I must confess that I have been unable to verify many of his 
statements and references. 

3 IT do not deny, of course, that Kircher formulated a “ doctrine of 
contagium animatum’’—and possibly more explicitly than his predecessors : 
but I do deny that it had any more objective basis than similar earlier 
guesses. The doctrine had no concrete foundation before L.’s discovery of 
real “ animalcules.’’ 


concept of a living “ contagion ” or infective agent—invisibly 
floating in the air at the time of epidemic pestilences, and com- 
parable with some kind of “insect”. Malaria, for example, 
was all too well known in classical times, and even rustic writers 
such as Varro‘ (116-27 B.c.) and Columella (florwit ca. A.D. 50) 
cuessed that the “insects” abounding in marshes have some 
causal connexion with “fever’’.* (The ancients even used 
mosquito-nets as a prophylactic.) At a much later date 
Lancisi (1718) developed a more coherent and modern theory 
of malarial infection: yet even in his hands it remained nothing 
but an ingenious speculation.’ The true aetiology of malaria 
has become known only in the last fifty years. In Leeuwen- 
hoek’s day both the malarial parasite and its mode of 
transmission by the mosquito were still wholly unknown to 
mankind, and the guesses of his predecessors and contem- 
poraries have really no bearing upon his own discoveries. 
Nobody before Leeuwenhoek ever saw a living protozoon, and 

1 Marcus Terentius Varro (who was no mere husbandman) is particularly 
noticeable because of his antiquity. He is frequently cited, but seldom 
correctly. In all his extant works there appears to be but one passage 
bearing on the aetiology of malaria: and as most editions of his writings 
are rare, and as the passage in question is very short, I may quote it here. 
Discussing sites appropriate for a country house, Varro notes certain places 
to be avoided (such as the banks of a river—apt to be too cold in winter 
and unhealthy in summer) and then adds: ‘‘ Attention should also be paid 
to any marshy places thereabouts ; both for the same reasons, and because 
[they dry up,] certain minute animals grow there, which cannot be detected 
by the eye, and which get inside the body from the air, through the mouth 
and nostrils, and give rise to stubborn distempers.” (Advertendum etiam 
siqua erunt loca palustria, et propter easdem causas, et quod [arescunt,] 
crescunt animalia quaedam minuta, quae non possunt ocult consequi, et per 
aera intus in corpus per os, ac nares perveniunt, atque efficiunt difficilis 
morbos.) Of. Varro, lib. I, cap. XII (Script. Rez Rust., ed. 1543, p. 54 recto). 
The words in square brackets should probably be omitted—arescunt being a 
MS. misreading or dittography of the word following.—Since writing the 
foregoing note I find there is now an excellent English edition of Varro by 
Storr-Best (1912): nevertheless, I let my own translation of the passage 

2 The references to malaria in the Latin classics are mostly collected in 
the recent posthumous work of Celli (1925), while the Greek literature has 
been ably reviewed by Jones (1909). 

3 Lancisi actually refers to L.’s discoveries in order to prove the existence 
of such extremely minute animalcules as he himself postulated. Cf. op. cvt. 
p. 46. 




all early speculations about the relation of “insects” to 
malaria belong properly to the -prehistory of entomology—not 
to that of protozoology. 

The whole history of bacteriology has recently been so 
admirably written by Bulloch (1930) that I can add nothing to 
his account of its origins.” He has shown quite clearly that 
real bacteriology (like real protozoology) began with Leeuwen- 
hoek’s discoveries, though it was preceded by a long period of 
speculation on the causes of contagious diseases. Some early 
writers, it is true, made astonishing guesses at the existence of 
bacteria—particularly Fracastoro (1478 or 1483—1553), whose 
hypothetic “ seminaria”’ bear a remarkable resemblance to 
modern ‘germs’ or “microbes”.? But nobody before 
Leeuwenhoek ever saw a bacterium with his own eyes. 
Nebulous though ingenious notions about invisible living 
organisms floated in the air for some thousands of years : but 
it required the untutored genius of a Leeuwenhoek to condense 
them—single-handed and with only his own little home-made 
‘““microscopes”’—into the concrete realities of present-day 
laboratories and text-books of bacteriology. 

Another point should not be overlooked in this connexion. 
When Leeuwenhoek announced his discovery of the 
“animalcules”” in various waters and infusions, it was 
universally regarded as something entirely new. Yet the 
earlier writings of Kircher and others had already been public 
property for some years. Why, then, were contemporary 
‘“ philosophers ’”’ astounded at Leeuwenhoek’s “ discoveries ”»— 
if they were not real discoveries? And why did some 
contemporary and later critics dispute his observations ? 
Why did no author of his time—including Kircher, who was 
still alive and busy writing—claim priority? It is surely 
strange, to say the least, that nobody before Loffler in 1887 
ever connected Leeuwenhoek’s concrete discoveries of 1676 
with Kircher’s random speculations and “experiments” of 1658. 

1 T may note, however, that I have studied most of the early writings 
mentioned in this fine and accurate work: but as I agree entirely with its 
conclusions, and as it has an authority far beyond anything to which I can 
pretend, I shall here dispense with all other references to the subject. 

2 I cite the work of Fracastoro because I have devoted particular atten- 

tion to his writings, owing to their great historic interest. On Fracastoro 
see also C. and D. Singer (1917). 


All Leeuwenhoek’s contemporaries regarded him as 
unquestionably the discoverer of his “little animals”. But 
his discoveries were soon confirmed by Hooke—as we have 
already seen—and by several other “philosophers”. In the 
last decade of the XVII Century the work of Buonanni' (1691) 
appeared, containing the first pictures of free-living ciliates, 
but reaffirming the doctrine of spontaneous generation—a 
small advance and a big step backwards at the same time. 
Of much greater importance were the papers by King’ (1698) 
and Harris * (1696), who both saw and described a variety of 
free-living protozoa and bacteria—tfrankly in imitation of 
Leeuwenhoek, but adding new facts and some original 
speculations. Of far less value, protozoologically, were the 
notes by Gray * (1696, 1697), who observed protozoa with his 
ingenious “ water-microscope” but gave only a slight account 
of what he saw. These five men—Hooke, Buonanni, King, 
Harris, and Gray—must all be regarded as belonging to the 
first generation of protozoologists. 

But by far the greatest scion of this generation still 
remains unknown to us by name. In two anonymous 
English publications’ which appeared in the Phil. Trans. in 
1703 are to be found some amazingly good figures of free- 

1 Filippo Buonanni, alias Philippus Bonannus (1638-1725), an Italian 
Jesuit priest. 

2 Sir Edmund King (1629-1709), M.D.; physician to Charles II, whom 
he attended during his last illness. He was elected F.R.S. in 1666. 

* The Rey. John Harris (1667 ?-1719), D.D., rector of Winchelsea in 
Sussex, F.R.S. (1696). Author of Lexicon Technicum (1704). 

* Stephen Gray (?-1736) was a physicist, who published a number of 
papers in the Phil. Trans. He was not made a Fellow of the Society 
until 1732. 

> See Anonymus (1703,1703a). The first paper consists of extracts from 
several letters written in 1702 and “communicated by Sir C. H.” [= Sir 
Charles Holt, not a Fellow] : the second comprises two other letters (1703) 
from “a Gentleman in the Country ”, communicated by “ Mr. C.” [probably 
John Chamberlayne]. All these letters were really written by the same 
person, whose identity I have vainly endeavoured to discover. The letters 
themselves are not in the Society’s archives or the British Museum (so far 
as I have been able to ascertain), and all the documents relating to them 
appear to have been destroyed. In view of their great interest, I have made 
repeated attempts to discover their authorship; but every clue has proved 
unavailing, and I fear that “The Gentleman in the Country” covered up 
his tracks on purpose—in order to remain anonymous for ever. 


living protozoa and bacteria, and diatoms '—confirming and 
amplifying many of Leeuwenhoek’s findings and accompanied 
by a commentary, light-hearted and conversational, which 
shows nevertheless remarkable insight and ability. The 
pictures were far ahead of anything previously published, and 
are sufficient alone to establish their draughtsman as Hldest 
Son of the Father of Protozoology. 

Only one other protozoologist of Leeuwenhoek’s period 
deserves notice here—Louis Joblot (1645-1723), a French- 
man. His observations were first published in 1718,’ and 
attracted little notice at the time: but his book is, in fact, 
the first special treatise on the Protozoa, and it contains 
descriptions and figures of many forms not previously 
described. A recent writer* has tried to show that Joblot 
was not merely a follower of Leeuwenhoek, but actually his 
equal—an independent co-discoverer of the Protozoa. But 
such a suggestion is manifestly groundless. There is no 
evidence that Joblot studied the Protozoa as early as the 
time when their discovery was announced by Leeuwenhoek ; 
and the appearance of his book in the next century—only five 
years before they both died—definitively assigns his publication 
to a later generation. In Joblot’s writings there is no direct 
reference to Leeuwenhoek’s discoveries, but much internal 
evidence of imitation.’ 

I have already had occasion to note’ that Leeuwenhoek 
himself made no application of his discovery of “‘ microbes’”’ 
to medical doctrines of contagion. He discovered protozoa 
and bacteria not only in waters and infusions but also in the 

1 Tabellaria—the first account and figures of this organism. Most of 
the other figures are equally easily recognizable. 

2 On Joblot see especially Fleck (1876), Cazeneuve (1893), Boyer (1894), 
Konarski (1895), Brocard (1905), and Dobell (1923). I may note here that 
the work of Sturm (1676), cited by Ehrenberg and others as containing 
contemporary observations on “‘infusoria’’, really deals only with insects 
and nematodes—not with protozoa. It should not be quoted in this 

3 This work is now very rare, and is better known from the much later 
and comparatively common edition of 1754. 

4 Konarski (1895). 

° Cf. Dobell (1923). 

* See p. 230 supra. 


bodies of living animals—including man: but he never in his 
writings suggested, so far as I am aware, that his discovery of 
such “animalcules” threw any light upon the aetiology of 
morbid infections or furnished, for the first time, an objective 
basis for the old speculations regarding the existence of 
“living germs” of diseases—seminaria morborum, contagium 
vivum, contagium animatum, and the like. Yet this applica- 
tion of his findings was immediately made by others. Within 
a few months of the appearance of his Letter 18, announcing 
the discovery of the “little animals” in all manner of liquids, 
we find “an observing person in the country” writing to the 
editor of the Philosophical Transactions as follows': ‘‘ Mr. 
Leewenhoecks Microscopical Discoveries are exceeding curious, 
and may prompt us to suspect, that our Air is also vermicu- 
lated, and perhaps most of all in long Calms, long-lasting 
Eastern Winds, or much moisture in Spring-time, and in 
seasons of general Infections of Men or Animals.” 

As soon as this possible connexion between demonstrable 
“animalcules” and hypothetic infectious “germs” was 
suggested, it became almost commonplace : its theoretical im- 
plications and its obvious practical applications were henceforth 
recognized. Yet nobody made any real use of them during 
the next century anda half. Mankind possessed the necessary 
data, and was inspired—as usual—by the appropriate ideas : 
but the course of history has shown that both knowledge 
and notions arrived prematurely. We should not blame 
Leeuwenhoek, therefore, for making discoveries before they 
could be appreciated properly either by himself or by the world 
at large. Rather should we censure, I think, those modern 
writers who do not take his work into consideration when 
discussing present-day problems. ‘To me it is incomprehensible 
how one author in my lifetime could have defended a thesis on 
Parasitology in the XVI and XVII Centuries,’ and another 
could have written a book on The Discovery of the Microbic 

1 See Anonymus (1677). Cf. also the words of Slare (1683), quoted 
already on p. 230. 

2 Rémignard (1902). This dissertation—approved by the great Raphael 
Blanchard—contains only two ridiculous references to L. The first (p. 55) 
merely alludes to the fact that he did not discover Demodex, while the 
second (p. 63) informs us that he believed in the spontaneous generation 
of frogs. 


Agents of Disease," and yet could both have ignored all 
Leeuwenhoek’s discoveries entirely. His work undoubtedly 
has an important bearing on the history of both these 

Notwithstanding such present-day neglect, Leeuwenhoek’s 
discoveries were utilized by contemporary theorists. I may 
mention particularly Benjamin Marten,’ who published in 
1720 (three years before Leeuwenhoek died) a most curious 
treatise to which attention has recently been directed by Singer 
(1911). In this book Marten, by assuming that tuberculosis 
is caused by invisible “ animalcula”’ like those discovered by 
Leeuwenhoek, develops a theory of the pathogenesis of this 
disease remarkably similar to current conceptions. In many a 
passage, if one substitutes “ Bacillus tuberculosis” for 
“animalcula”’ his statements are in close agreement with the 
views expressed in modern bacteriological and pathological 
works. As a prognostication, or even as a mere tour de force, 
Marten’s book is notable: but he himself never saw the 
tubercle bacillus, and his writings had no influence on the 
history of bacteriology. 

In recent times a claim to recognition has also been made 
for the French physician J.-B. Goiffon (1658-1730), of Lyons. 
Molliére (1886) calls him “wn précurseur des théories 
microbiennes”’ on the strength of a dissertation on the 
plague which he published in 1722. In this Goiffon 
propounds the theory that plague is caused by an invisible 
virus (vénin)—probably some kind of “insect” “—which floats 
in the air and penetrates into the blood either through the 
pores of the skin or else through the mouth or nose. But 
Goiffon never attempted to see such “insects” himself, and 
makes no mention of the real “animalcules”’ already well 
known at that date (through the discoveries of Leeuwenhoek 

1 Grober (1912). This German writer’s ignorance of L.’s existence was 
possibly feigned, and due to a false patriotism: for though his book bears 
evidence of considerable learning, its author had apparently never even 
heard of Pasteur also. 

2 Marten was a London physician about whom very little seems to be 
known. His book is excessively rare, and I am indebted to Dr Charles 
Singer for the loan of his own copy—the only one which I have studied. 
There is another, however, in the British Museum. 

3 Tn one place he actually conceives of it as possessing wings ! 


and his imitators). His own speculations are not particularly 
prescient or original, and appear to have but little relation 
to modern conceptions. I regard Goiffon’s dissertation as 
historically negligible: in any case, it was without influence 
upon the course of bacteriology or protozoology. 

I cannot omit to mention, in the present connexion, an 
extraordinary effort in pseudo-microbiology published just 
after Leeuwenhoek’s death by a French quack doctor. This 
charlatan, who wrote under the initials ‘““ M.A.C.D.”, pretended 
to discover the “insects” responsible for all diseases, and to 
cure his patients by eradicating them by secret methods.’ 
He claimed to be following the system of an English physician 
who had learned of it in Persia: and he gave a comical 
description—accompanied by the crudest cuts—of no less than 
91 absurdly-named “little insects” which cause as many 
complaints. This imposture was exposed by Vallisneri,” in a 
posthumously published letter which is not generally known. 
I need make no further reference to it: I mention it only 
because certain learned authors have apparently taken this 
obvious bit of charlatanry for a serious contribution to 
microbiology or for genuine satire.’ It was certainly neither. 

There is no need, for present purposes, to trace in detail 
the history of our knowledge of Leeuwenhoek’s “little 
animals’? down to modern times. We are here concerned 
merely with the beginnings of protozoology and bacteriology : 
yet to see them as beginnings we must cast our eye also upon 
the later historical landmarks. As everyone knows, scant 
progress was made in the century following Leeuwenhoek’s 
death; though it is worth noting that the first scientific 

1 See M.A.C.D. (1726, 1727). I quote him (as is customary) under 
these initials, though his real name, according to Vallisneri (1733), was Boil. 
From the “ Privilége du Roy” at the end of his work, where the author 
is referred to as ‘le siewr A.C.D.’, it seems that the initial M. stands 
for Monsieur. Consequently, he ought properly to be catalogued as 
Pa ey ag 

“See Vallisneri (1733), Vol. III, p. 218. It is here explained how “Mr 
A. C. D.’ was able to impose upon his patients by showing them the 
“insects”? in their blood or urine through a trick microscope—which 
apparently exhibited the object mounted before it, but really showed 
protozoa out of an infusion. 

* Cf. Lesser (1738), Ehrenberg (1838), Bulloch (1930), ete. 


names' were assigned to protozoa by John Hill’ in 1752, and 
that the first serious systematic treatment of both protozoa 
and bacteria was attempted in 1773 by O. F. Miiller*— 
revising and amplifying the inadequate account of these 
organisms given by Linnaeus* (1758, 1767). These three 
writers—an Englishman, a Dane, and a Swede—were all very 
remarkable men, in very different ways; yet they had this in 
common that they all respected Leeuwenhoek. Even the 
cavalier Hill—a bitter critic of the Royal Society and all its 
works (which he nevertheless copied’ freely for his own 
profit)—was forced to allow his merits. In one place he says, 
for example, “Even Lewenhoeck the Father, as he may be 
called, of this Branch of Observation, is not without his 
Mistakes, tho’ there are many more in Proportion in all 
that have followed him”.° 

Hill was an amateur microscopist, and he made no original 
contributions of value to protozoology: but though Linné 
was a professional naturalist, he had equally little know- 
ledge of the Protozoa—notwithstanding he made the first 
attempt to classify the micro-organisms known in his day. 
But Miller was a systematist with a good working knowledge 
of the “‘ Infusoria.”‘ He applied Linné’s system to organisms 
which he had himself seen and studied: and he was, withal, an 

1 They were pre-Linnaean and not binominal: yet some of them—such 
as Paramecium—are still current. 

2 Much has already been written about ‘Sir’? John Hill (1716-1775), 
though nobody has yet duly appraised his contributions to protozoology. 
Cf. especially the Dict. Nat. Biogr., T. G. Hill (1913), and Woodruff (1926). 

* Otto Friderich Miiller (1730-1784). Cf. Dansk Biogr. Lewx., XI, 594. 
The most recent estimate of him (chiefly as a botanist) is that of Christensen 
(1922, 1924). Biitschli fully appreciated his protozoological works, but no 
other recent student of the protozoa has attempted to assess or even interpret 
all his extremely important observations on these organisms. 

* Carl von Linné (1707-1778). For his life see especially Daydon 
Jackson (1923). 

° As an instance I may note that most of Hill’s figures of protozoa 
(1752) were boldly copied without acknowledgement from the anonymous 
writer of 1703—from the Phil. Trans. which he so affected to despise ! 

® Hill (1752a), p. 94. 

" Miiller’s “ Animalcula Infusoria”’ were a motley crew of microscopic 
creatures, comprising not only all the protozoa and bacteria then known, 
but also worms, rotifers, algae, and other organisms. 


excellent observer. His wrong interpretations were inevitable 
at the time when he wrote: and when we remember that he 
made his observations mostly with the aid of simple lenses of 
English manufacture (probably much inferior to Leeuwenhoek’s), 
we can now only admire his accuracy. In my view, Miller was 
one of the great protozoologists of all time. He was also, for 
his period, a good bacteriologist—familiar at first hand with 
many bacteria—though he nowhere considers the possibility 
that any micro-organisms may be causally connected with 

Linnaeus’s views regarding protozoa and bacteria, and their 
relation to infectious diseases, are not easily ascertained. 
In the Systema Naturae (ed. X, 1758) he grouped all the 
known protozoa in his Class VERMHES and its last order 
ZoopHyTa. Apart from a few Foraminifera and Vorti- 
cellidae—placed under molluscs and polyps respectively—all 
the Protozoa which he recognized were comprised in the single 
genus Volvox, containing only two species. In his 12th 
edition, however, he elaborates this system somewhat, and 
assigns all the “ animalcules” then known to three ill-defined 
genera—Volvox, Furia, Chaos. All the “ infusoria”’ described 
in “the books of micrographers” (including Leeuwenhoek) 
are lumped together in a single species ‘“ Chaos infusorium”’ : 
but as an appendix he adds 6 doubtful kinds of “living 
molecules ”’ which he leaves to his followers to elucidate." The 
list 1s so curious, in many ways, that I must quote it here: ? 

The contagion of eruptive fevers ? 

The cause of paroxysmal fevers ? 

The moist virus of syphilis ? 

Leeuwwenhoek’s spermatic animalcules ? 

The aery mist floating in the month of blossoming ?* 
Miinchhausen’s septic agent of fermentation and 
putrefaction ? 

wine Os" "G8 

Dr Bulloch—who quotes the foregoing list in its original 

1“ obscurae . . . moleculae vivae . . . posteris relinquendae.” 

2 I translate the original Latin into English in order to be consistent : 
but all students of the history of protozoology and bacteriology are doubtless 
familiar with Linné’s own words. 

3 Meaning, of course, the month of May—which the Dutch also prettily 
call Bloeimaand. 


Latin—justly remarks (1930, p. 22) that it “is surprising to 
find Linné, 30 years after Leeuwenhoek’s death, placing in 
the same class spermatozoa and the ‘ethereal clouds in the 
time of flowering’’’; and he and others have been puzzled by 
Linné’s “ aethereus nimbus”’ (e, supra). But it is probably, I 
think, merely a reference to the anonymous English author 
of 1677." 

Linnaeus himself doubted whether all the then known 
protozoa” and bacteria (as we now call them) might not really 
be stages in the development of fungi, and he questioned their 
relation to diseases. Similar vague suggestions were mooted 
in the dissertations of some of his pupils (Bostrém, 1757; 
Nyander, 1757; Roos, 1767): but what Linnaeus himself 
believed I cannot discover. I think he had no definite ideas ; 
for though he was certainly not blind to the possibility that 
‘“microbes’”’? may cause diseases, he was also sceptical and 
unable to make up his mind. In his own thesis for his degree 
(1735) he argued that “intermittent fevers” are caused by 
drinking water contaminated with clay, though in 1757 he 
apparently approved Bostrém’s thesis contending that the 
cause was “bad air” or faulty sanitation. Yet at the same 
time he envisaged the existence of “exanthemata viva” 
(cf. Nyander), and ten years later (cf. Syst. Nat., and Roos, 
1767) was seemingly still sitting on the fence. In my view, 
Linné and his pupils never understood Leeuwenhoek’s “ little 
animals,’ and all their attempts at systematization merely 
created confusion. ‘Their works are of great historic interest, 
however, in showing how far professional biologists and medicos 
had profited by Leeuwenhoek’s “amateur” labours a century 
after he announced his first discoveries. 

The only other authors of this period who call for passing 
notice here are three Germans—of very different merits. First, 
Résel von Rosenhof,’ a miniature-painter who published some 
admirable descriptions and figures of protozoa in 1755: secondly, 

1 Quoted on p. 373 supra. 

2 The name “ Protozoa” was first used by Goldfuss (1817): but his 
group so named included not only the “ Infusoria” but also “ Lithozoa”’, 


‘“ Phytozoa’’, and “ Medusae”’. 

3 August Johann Résel von Rosenhof (1705-1759). His life by Kleemann, 
his son-in-law, is prefixed to the fourth volume of his Insecten-Belustigungen. 
Cf. also Miall (1912), p. 293 sq. 


Ledermiiller,’ a lawyer and amateur microscopist: thirdly, the 
physician Wrisberg°— better known as an anatomist and 
obstetrician—who published a dissertation on ‘“ Animalcula 
Infusoria” in 1765. The work of Ledermiiller (1760-1765) is 
really almost negligible, so far as the Protozoa are concerned. 
It is chiefly remarkable for being constantly misquoted as the 
first publication in which the indefinite term “ Infusoria ” was 
employed*: but so far as I have been able to discover, the 
word occurs nowhere in Ledermiiller’s long-winded writings. 
It was really first used, I believe, by Wrisberg in the booklet 
just mentioned, which—though always cited as a classic— 
contains little of protozoological importance or novelty. 

The much-quoted English works of Adams* (1746) and 
Baker ° (1742, 1743, 1753, etc.) are of no account. Both were 
copyists and compilers, who drew largely upon Leeuwenhoek’s 
publications for their own purposes. Baker’s books, however, 
enjoyed a great vogue among the amateurs of his day, and 
were translated into several foreign languages. In the opinion 
of Harting (1876)—which seems well founded—the Dutch 
translations of his popular works on the microscope were, 
indeed, responsible for a sudden revival of interest in Leeuwen- 
hoek in Holland: for it is a singular fact that on his death 
Leeuwenhoek was not only almost immediately forgotten by 
the learned world but even by his own countrymen, and the 
memory of his achievements has therefore undergone periodic 
-resuscitations both at home and abroad. 

The latter half of the XVIII Century was enlivened by 
the classical controversy between Spallanzani® and Needham 


1 Martin Frobenius Ledermiiller (1719-1769). For his life see the 
recent sketches by Willnau (1921, 1926). 

* Heinrich August Wrisberg (1739-1808). His life will be found in the 
Allg. Dtsch. Biogr. and Hirsch’s Lexikon. 

* Biitschli—usually so accurate—appears to be responsible for the origin 
of this erroneous statement. Ledermiiller actually spoke only of “infusion 
animalcules”’ in the vernacular (“Infussions Thierlein”; op. cit. Vol. I, 
p. 88). 

* George Adams, the elder (?-1773) : mathematical instrument-maker to 
George III. See Dict. Nat. Biogr. 

° Henry Baker, F.R.S. See note 1 on p. 318 supra. 

° The Abate Lazzaro Spallanzani (1729-1799)—too great and famous an 

ornament of Italian science to require annotation here. (But the reader 
may consult with profit the recent note by Bulloch, 1922.) 


(supported by Buffon)' on the subject of spontaneous generation. 
This dispute is too familiar for reconsideration here: and 
I need only note that Spallanzani successfully defended 
Leeuwenhoek’s position—though he paid little attention to 
his Dutch predecessor—and was able to support their mutual 
belief by many admirable new experiments. But despite his 
great experimental skill and instinctive appreciation of scientific 
principles, Spallanzani possessed no real knowledge of protozoa 
or bacteria. Most of the organisms which he studied can now 
be recognized only with difficulty, or not at all, from his 
descriptions. Spallanzani was a great experimentalist and 
physiologist, but no morphologist or systematist. Needham’s 
contributions, however, to all branches of protozoology and 
bacteriology may not unfairly be now assessed as nil. He 
may have been a good Catholic, but he was a hopelessly bad 
protozoologist and bacteriologist. 

Although the middle of the XVIII Century produced 
numerous confirmations of Leeuwenhoek’s protozoological 
discoveries, they were not—at that time—usually so regarded: 
they were rather considered as novelties. Nevertheless, 
Antony’s marvellous researches on the multiplication of 
Volvox and other phytoflagellates were extended by the work 
of Trembley’ (1744a, 1747), de Saussure * (1769), Ellis * (1769), 
and Corti’ (1774)—two Genevese, an Englishman, and an 
Italian. Germany, soon afterwards, also contributed her 
share to protozoology through the work of Gleichen* (1778), 

? John Turberville Needham (1713-1781), a British catholic priest who 
spent most of his life in France and Belgium. Elected F.R.S. in 1747. 

2 Abraham Trembley (1700-1784), sometime tutor to the sons of 
William Bentinck, English resident at The Hague. Later he came to 
England, and was elected F.R.S. in 1743. 

3 Horace Bénédict de Saussure [sew Desaussure ] (1740-1799), naturalist 
and celebrated Alpinist. For his life see especially Senebier (1801). He 
was elected F.R.S. in 1788. 

* John Ellis (1710 ?-1776), government agent in the West Indies, and 
author of the well-known work on Corallines. Elected F.R.S. in 1754. 

* Bonaventura Corti (1729-1813), a catholic priest. Professor of 
Natural History at Reggio, and a friend of Spallanzani. One of the earliest 
students of the Cyanophyceae, and the discoverer of Spirulina. 

* Baron Wilhelm Friedrich von Gleichen-Russworm (1717-1783). 


who re-examined the organisms in infusions, and of Eichhorn ' 
(1775, 1783), who discovered the first heliozoon (Actino- 
sphaerium). But Holland’s only representatives during this 
period were Job Baster (1759), who recorded some trifling 
observations on vorticellids, and Martinus Slabber (1778) who 
rediscovered, redescribed, and first depicted Noctiluca.” Yet 
it is a remarkable fact that—apart from Miiller, who was in 
this connexion mainly a nomenclator and systematist— 
nobody arose anywhere for more than a century following 
Leeuwenhoek’s death who can now fairly be called a bacterio- 
logist. For 150 years from the date of their discovery 
the Bacteria were strangely neglected. Mankind remained 
inexplicably blind to their importance, and almost to their 
very existence. 

From the standpoint of protozoology and bacteriology the 
first quarter of last century is a blank. At the end of this 
barren period, however, a revival of interest in Leeuwenhoek’s 
“little animals” set in—a revival which led, with gradually 
increasing momentum, to the enthusiastic development of our 
modern sciences. It is now difficult to place oneself in the 
position of a zoologist or physician a hundred years ago: 
progress in our knowledge of all “ microbes’ has since been so 
rapid and so revolutionary. In 1832, Bory de St.- Vincent * had 
just published his reclassification of the “ Infusoria ”—which 
he needlessly renamed ‘‘ Microscopica’’ *—and Ehrenberg’ was 
busy cataloguing the booty collected in his travels: his 
monumental monographs were just germinating in the form of 

1 Johann Conrad Hichhorn (1718-1790), pastor of the Church of 
St Catharine at Danzig. 

2 Noctiluca, one of the chief organisms causing phosphorescence on the 
surface of the sea, was discovered by the Englishman Joseph Sparshall, 
of Wells in Norfolk, whose observations were recorded by Baker (1753, 
p. 402 sq.). 

* Colonel J. B. Bory de St.-Vincent (1778-1846), soldier, politician, 
traveller, and naturalist. For his life, works, and correspondence see 
Lauzun (1908). 

4 “ Microscopiques.” I believe Bory borrowed this term—as he did so 
much else—from Miiller (1773, p. 4: “microscopica dicuntur, quod unice 
lenticulae amplificantis ope videntur’’). 

° Christian Gottfried Ehrenberg (1795-1876), of Berlin. The fullest 
biography is that of Laue (1895). See Dobell (1923a) for further references. 


tentative preliminary papers.’ His huge final treatise of 1838, 
together with its comparatively small but devastating corrective 
by Dujardin’ in 1841, forms the real foundation of modern 
Protozoology. But the first experimental work on trans- 
missible microbic diseases was probably that published in the 
same period by Bassi * (1835), while the first on any protozoal 
infection came much later from Pasteur (1870). Both of these 
experimenters studied, singularly enough, no well-known 
maladies of man, but certain obscure “epidemics” of silk- 
worms—“ moscardino”’ and “ pébrine”’ respectively.’ 

It is not my purpose now to trace the history of Proto- 
zoology and Bacteriology during the last hundred years, so I 
shall leave the subject at the moment when our modern sciences 
commenced. The authors I have mentioned, and the works 
which they performed, are chronicled merely to remind the 
reader of certain salient events which cannot be overlooked if 
we would see Leeuwenhoek in his true perspective and 

Of Leeuwenhoek’s discoveries in sciences other than 
Protistology I am not competent to speak. I observe, however, 
that he is usually most praised by those most qualified to judge. 
Those authors who decry his observations generally reveal 
themselves, at the same time, ignorant of himself and his 
works. Asan instance I may cite the opinions expressed by 
certain botanical writers. Two careful Dutch authors— 
van Hall (1834) and Bolsius (1903)—find much that is original 
and admirable in Leeuwenhoek’s studies of plants: but the 
more famous German botanist Sachs (1875), whose knowledge 
of Leeuwenhoek was obviously not profound, says that “ 
the whole, all his numerous communications, in comparison 

1 T possess and have studied all of these, though I do not cite them here. 

2 Félix Dujardin (1801-1860), Professor of Zoology at Rennes. For his 
life see Joubin (1901). I have also studied—though I do not cite—the 
earlier works of this admirable protozoologist. 

® Agostino Bassi (1773-1856), of Lodi. See his Opere (1925), recently 
reprinted and edited, with a remarkable introduction by the late Prof. 
B. Grassi; who sums up his review with the statement that “it is proved 
that parasitology, like many other branches of knowledge, had its cradle 
in our own Italy: foreigners have merely recognized and perfected it.” 
Nevertheless, no Italian saw protozoa or bacteria before the year 1674. 

* Moscardino is now supposed to be caused by a fungus (Botrytis) and 
pébrine by a protozoon (Nosema)—both of doubtful systematic status. 


with Malpighi’s pleasing clarity and Grew’s systematic 
thoroughness, create a painful impression of superficiality 
and amateurishness.””* A similar opinion of Leeuwenhoek’s 
work in general has, moreover, been recently expressed by one 
of his own compatriots (Becking, 1924), who sees in him 
merely “a pair of eyes, a pair of hands, directed by other 
minds. For when his own mind tried to direct, he could 
produce nothing but chaos.” ‘This is surely a strange estimate 
of the almost wilfully independent Leeuwenhoek I know—who 
certainly produced something very different from chaos when 
he discovered the Protozoa and the Bacteria! But even for 
these discoveries Becking allows Leeuwenhoek little credit: he 
avers that “although he was the first to see bacteria, yeasts 
and protozoa, we can not look upon him as the founder of 
microbiology.” Despite his obviously great knowledge’ of 
Leeuwenhoek, and his own distinction in other branches of 
learning, I am unable to judge of Becking’s competence in 
protozoology—since he has not (to my knowledge) contributed 
as yet anything to the advancement of that science. His 
evaluation of Leeuwenhoek may, however, be contrasted with 
that of the only man of our times who possessed a profound 
knowledge both of the Protozoa themselves and of proto- 
zoological history. He not only respected and admired 
Leeuwenhoek’s work, but he even dedicated one of his own 
most important memoirs to his memory.” 

Other biologists have already honoured Leeuwenhoek in 
their own peculiar way by naming various organisms after him. 
It is true no protozoon or bacterium or other “little animal ” 

1 Sachs (1875), p. 264; translated. I have good reasons for believing 
that these words were actually plagiarized from an earlier and less-known 

2 Becking writes as one who knows all about L., and he says that “ the 
uncritical praise of his commentators and biographers can only be ascribed 
to an insufficient knowledge of his works and that of his contemporaries.” 
Considering Becking’s greater knowledge, I confess that at first I found it 
difficult to understand how he could refer to L. as “a humble lens-grinder ”’, 
who was ‘a patrician’s son”? and “had many children’’, ete. But such 
obvious misstatements of fact are to be explained, doubtless, by his con- 
viction that “What really matters in a biography is not the so-called 
biographical datum.”’ I differ from him in believing that accurate data are 
the szne qua non of any biography. 

3 Biitschli (1876). 


of his own discovering now bears his name:’ yet it has been 
bestowed—more or less permanently—upon a minute moth,’ a 
tiny mite,’ and an insignificant Australian flowering plant* .. . 
“cum rerum Natura nusquam magis quam wm minimis 
tota sit.” 

My personal estimate of Leeuwenhoek is based upon a 
study of his own works. [admit that [have not yet examined 
his numerous writings sufficiently, but I have read enough to 
realize that those people who ridicule him are generally 
ignorant, and usually reveal their own incompetence in the 
very act of denouncing his. Whilst professing to show us his 
faults they unintentionally pillory themselves. Leeuwenhoek 
and his disciples have now no need even to contradict state- 
ments such as “this physician described many things that he 
never saw,’ or “his assertions . . . sufficiently prove that 
he saw less through his microscope with his eyes than with 
his imagination:’’’? and nowadays we only laugh when we 
read this pronouncement by the self-appointed judge of the 
Royal Society—*‘ Lewenhoeck . . . had the good fortune 
to be one of the first People who worked at microscopical 
Observations, but we are to acknowledge at the same Time, 
that he has had the Honour of having stocked the Philo- 
sophical Transactions with more Errors than any one Member 
of it, excepting only his Successor in Peeping, Mr. Baker.” ° 

1 The name “ Pandorina leuwenhoekii’’, proposed by Bory de St-Vincent 
(1826, p. 22), is an invalid synonym of Volvox globator Linnaeus: while the 
same author’s ‘‘ Esechielina lewwenhoekii”’ (1826, p. 78) has been engulfed 
in the synonymy of Rotifer vulgaris. 

2 Oecophora leeuwenhoekella [Tineidae] F. v. P. Schrank, 1802. For 
the various spellings of the specific name see Sherborn (1927). Cf. also Isis 
(1839), p. 192. 

3 Genus Leewwenhoekia Oudemans, 1911. 

4 Levenhookia pusilla Brown, 1810. In proposing the genus, Robert 
Brown says (in Latin) that he dedicates it ‘to the memory of the most 
famous micrographer, in whose works there are many most beautiful 
observations on the structure of vegetables.” Brown’s spelling of the 
generic name is curious, and is evidently an attempt to reconcile Dutch 
orthography with Latin and with English pronunciation. Later emendations 
(such as ‘‘Leevenhokia’”’ van Hall, 1834) can hardly be regarded as 

° Jourdan (1822), Biogr. Méd., V, 561. 

® John Hill (1751), p. 156. The reference is to Henry Baker (see 
p. 318 supra), one of Hill’s pet aversions. 


At all times the name of Leeuwenhoek has been mentioned 
with respect by those who have really made his acquaintance. 
Even general historical writers’ are sometimes aware that he 
was one of the phaenomena of the XVII Century: and even 
in his own lifetime his claims to recognition were conceded by 
biological and medical authors. Leeuwenhoek was no 
‘physician ” or “ surgeon ’’, as he has so often been ridiculously 
styled: nevertheless, he was already called “celebrated” in 
Roukema’s Dictionary of Famous Physicians as early as 1706, 
and he now has a whole section to himself in Banga’s History 
of Medicine and its Practitioners in Holland (1868) and in 
Hirsch’s Biographical Lexicon of Distinguished Doctors of all 
Times and Peoples (1886). The great and learned Leibniz 
paid attention to his discoveries, which were not without 
influence upon his own philosophy: indeed, the abstract 
‘““monads”’ of the Monadology are not altogether unrelated to 
Leeuwenhoek’s concrete “animalcules”.” But to trace 
Leeuwenhoek himself through all the misunderstandings and 
misquotations and muddles of the multitudinous authors who 
have utilized his discoveries for their own ends, is a task 
beyond my competence; and for my present purpose it is, 
fortunately, unnecessary. 

Leeuwenhoek will be finally judged by his own writings, 
and not by anything that other people say he wrote. He has left 
us a great mass of records—both published and unpublished 
from which we can now extract what we please. I have 
endeavoured to recover from them all his observations on the 
Protozoa and the Bacteria, and to set in order his inchoate and 
uncorrelated findings in a manner which may fairly convey 
their import and importance to present-day students. ‘To me 
his words, when judicially weighed in the scales of con- 
temporary and recent knowledge, prove conclusively that he 
was the first protozoologist and the first bacteriologist. He 
has had thousands of followers and imitators, and was pre- 
ceded by a few prophetic precursors; but his own true place 
in Protozoology and Bacteriology appears to me incontro- 

1 For example, Hallam in his Literatwre of Europe (published first in 

2 Leibniz also mentions L. in his Théodicée (published in 1710). His 
correspondence with L. is discussed by Ehrenberg (1845): but the first author 
who appears to have realized Leibniz’s intellectual debt to L. is Radl (1905). 



vertible. He was the originator of everything we now know 
about ‘‘ microbes ’’, and of all that will ever be known about 
these organisms. To say that he is “not the founder of 
microbiology . . . although he was the first to see bacteria, 
yeasts, and protozoa”? may sound very knowing, and may 
satisfy those who seek paradox and literary effect: but every 
workaday bacteriologist and protozoologist knows that it is 
sheer nonsense. One might equally well say that Columbus 
did not discover the New World because he left no account of 
New York. 

In the foregoing pages I have done my best to portray 
Leeuwenhoek and to chronicle some of his great discoveries 
anew in his own words. If I have also attempted to represent 
other leading figures in the historic scene wherein he himself 
appears, it is because I realize that he can be recognized in 
his true character only when the other actors are ranged 
beside him on the stage. It is not for me, or any other living 
man, to design or paint the scenery or to dress the players or 
even to clap or hiss their exits and their entrances. I can 
but strive to discharge with fidelity the humbler office of the 
man who manipulates the limelight—whose duty is to show, 
in just illumination, the performers in a drama which I neither 
did nor ever could compose, and of whose intricate plot I have 
but the roughest working knowledge. 

I have always endeavoured to regard Leeuwenhoek 
objectively and dispassionately, but I am conscious that I 
have not always succeeded: for whenever I listen to his talk 
about “little animals” I am carried away by the unintentional 
eloquence of his discourse. He speaks an ungrammatical and 
old-fashioned language which is not my mother-tongue, and 
which I have learned painfully and as yet imperfectly : but he 
also echoes a language which I hear oftener than any other— 
that of the “little animals” themselves. I have spent all my 
working life trying to understand them, but I still know no 
more than old Antony knew—just enough, in fact, to inspire 
me with the enthusiasm to continue listening and labouring, 
but never enough to feel satisfied with my interpretations. 
I have unbounded admiration for Leeuwenhoek because he 
heard and interpreted things that I, unaided, could never have 
discovered, and hit on problems—during quiet nights in his 
own private closet—of which neither he nor I can ever know 
the final solution. 


One of Leeuwenhoek’s own countrymen has recently called 
me his “ greatest living admirer.”* I am proud to admit the 
accusation, and this book gives some of the grounds for my 
conceit. But the foregoing pages are not meant as an appeal 
to the reader’s emotions—only to his reason. “ How Dogma- 
tical soever my Assertions may seem to be, yet do I not affect 
the unreasonable T'yranny of obtruding upon the Faith of any. 
He that speaketh Reason, may be rather satisfied, in being 
understood, than believed.” ” Consequently, if my poor labours 
succeed in robbing me of a title which I hold but temporarily 
and precariously, they will not have been wholly in vain; and 
I shall be the first to rejoice when I am deposed from a 
position which I do not deserve, cannot maintain, and have 
never sought. 

As I aim at nothing but Truth, and, so far as in me 
lieth, to point out Mistakes that may have crept into 
certain Matters; I hope that in so doing those I chance 
to censure will not take it ill: and if they would expose 
any Errors in my own Discoveries, I’d esteem it a 
Service; all the more, because ’twould thereby give me 
Encouragement towards the Attaining of a_ nicer 

1 Dr W. H. van Seters, as reported in the Nieuwe Rotterdamsche Courant 
of 13 July 1926 (Nr. 83, blz. 6). 

2 Nehemiah Grew (1672), last lines of Preface. 

* Translated from L.’s Letter 135 (25 Dec. 1700): published in Brieven, 
Sevende Vervolg, p. 307. 



HERE is still no complete edition of all Leeuwenhoek’s 
letters: and of those already published there are so 
many versions that specific reference to any particular 

passage is often a matter of grievous difficulty. The biblio- 
graphies already printed by Gronovius (1760), Pritzel (1872), 
and many others, are so incomplete and otherwise imperfect 
as to be almost worthless. But a committee of experts has 
lately been formed in Holland with the object of printing or 
reprinting all Leeuwenhoek’s extant writings; and we may 
therefore hope that the material for a full and accurate biblio- 
graphy will shortly be collected and collated, and placed at the 
disposal of the public. 

In the meantime, since I have not the leisure or learning 
—still less the funds—of the Dutch committee, but owe it to 
my readers to give the sources of my own information, I can 
only offer the following record of those writings which I have 
myself consulted. For the present work I have had to study 
every available manuscript and publication in order to collect 
the passages relating to protozoa and bacteria, and I have 
therefore had to catalogue every discoverable letter and collate 
all its versions. But my own private list of Leeuwenhoek’s 
writings, so compiled, is still far too faulty to print here—and 
also far too long: and moreover this is obviously not the place 
to publish such a compilation. I therefore give now only the 
briefest indication of my sources for the assistance of fellow- 


The Leeuwenhoek Manuscripts in the possession of the Royal 
Society: 4 volumes, containing also numerous translations, 
drawings, and other relevant material. Lmperfectly catalogued 
by Halliwell-Phillipps (1840). Referred to, here throughout, 
as ‘ Roy. Soc. MSS.” Together with a few letters among the 
Boyle MSS. and elsewhere in the Society’s archives, and 


including fragments and copies of letters addressed to others, 
they amount approximately to 200. At present I cannot 
enumerate them more exactly. (Their number is grossly 
overstated by most previous authors, who apparently count 
originals and translations and printed proofsheets as “ original 
manuscripts.) As these manuscripts form the basis of the 
present work, I may add the following notes upon them: 

The Roy. Soc. MSS. (mostly Dutch) were very incompletely 
and imperfectly printed in the form of extracts or abstracts, 
in English or Latin, in contemporary numbers of the Philo- 
sophical Transactions and Hooke’s Philosophical Collections 
(which replaced the Transactions between Vol. XII, 1678-9, 
and Vol. XIII, 1682-3). These periodicals contain approxi- 
mately 120 printed “ extracts’ from Leeuwenhoek’s letters, 
though the “extracts” do not represent exactly the same 
number of original letters. The printed versions will all be 
found in Phil. Trans. Vol. VIII (1673) to Vol. XXXII (1723) 
inclusive [none in Vols. XVI and XXX], and are indexed— 
more or less accurately—by Maty (1787). Similar “ extracts” 
from 2 letters were included in Hooke’s Lectures and Collections 
(1678)—reprinted in his Lectiones Cutlerianae (1679)—and of 
3 others in his posthumous Philosophical Haperiments and 
Observations edited by Derham (1726). 

Many of these manuscripts were published in full, however, 
in Leeuwenhoek’s printed Dutch and Latin collective works, 
and 14 of the previously wholly unpublished early Dutch 
letters have just appeared in Opuscula Selecta Neerlandicorum, 
Vol. IX (1931): while two of the letters sent to the Royal 
Society, together with a fragment of Letter 116, have passed 
somewhat mysteriously into the Sloane MSS. now preserved 
in the British Museum. (I say ‘mysteriously’ because the 
honourable Sir Hans Sloane, M.D., had no obvious right to 
incorporate any of Leeuwenhoek’s original letters, addressed 
to him as Secretary of the Society, in his own private 

Other surviving manuscripts of Leeuwenhoek are known to 
me only through more or less recently printed versions or 
descriptions. I have not yet been able to study all the 
originals, but note their existence here for the help of others: 

The Leeuwenhoek Manuscripts in the Huygens Collection at 
Leyden (University Library). Eight in number, and now 
printed in Guvres Complétes of Chr. Huygens (see especially 



Vol. VIII; 1899) or by Vandevelde and van Seters (1925). 
Also partially printed or abstracted by Snelleman (1874), 
Haaxman (1871, 1875), Vandevelde (1924a). [Some of the 
MSS. known to Haaxman (1875) have seemingly since 
disappeared. They were apparently removed by a former 
librarian, who claimed them as his private property.}| A 
complete list of these MSS., with 5 others (one published) 
which I have not been able to trace further, is given by 
Harting (1876, pp. 121-3). 

The Leeuwenhoek Manuscripts in the National Library at 
Florence. These letters (about 15) were all addressed to 
Magliabechi,, and have been partly printed by Targioni- 
Tozzetti (1745) and Carbone (1930). [The latter erroneously 
includes among them a letter written by Leibniz,’ and 
previously published as such by Targioni-Tozzetti (1746). ] 

Four [? three] Leeuwenhoek Manuscripts in the Municipal 
Museum at The Hague. They are discussed, and their contents 
described, by Servaas van Rooijen (1905). 

Manuscript of a Letter (dated 3 [?13] March 1716) to 
Leibniz. Preserved among the Leibniz MSS. at Hanover 
(fide Khrenberg, 1845), together with drafts of 3 letters from 
Leibniz to Leeuwenhoek. [This letter—Send-brief XX—was 
published in full in L.’s Dutch and Latin collected works. | 


No serious attempt has yet been made by any bibliographer 
to collect and collate all Leeuwenhoek’s numerous printed 
letters. His published writings have been, indeed, the despair 
of all authors who have had occasion to refer to them; and I’ 
do not, therefore, pretend to describe or enumerate all their 
many versions here. 

Leeuwenhoek himself published in his lifetime 165 letters 
(not counting letters contained within letters): and to these 

1 Antonio Magliabechi (1633-1714), a Florentine scholar of prodigious 
learning. This remarkable man—of poor parentage—became librarian to 
Duke Cosmo III of Tuscany: and though he published nothing during his 
lifetime he is said to have been himself “ a walking library ” (including the 
dust and cobwebs, apparently). L. wrote to him because he had heard that 
he was then the most learned man in Italy: and he also dedicated to him 
his Latin edition entitled Arcana Naturae Detecta (1695). 

2 Cf. p. 46, note 1, and p. 359 supra. 


he assigned numbers—in chronological order. He published 
them, however, in two separate series—the first numbered 
with arabic numerals, the second with roman. But the first 
series began with No. 28* (not No. 1) and ran to No. 146, and 
thus consisted of 119 letters in all: while the later series 
(46 letters) was consistently numbered from I to XLVI. 
This, in itself, is apt to cause confusion: but the difficulty of 
collation is increased because the letters were not originally 
published always in strict chronological order, and were 
frequently, on their first issue, not numbered at all. Their 
seriation can therefore be determined only by their dates, or 
by the numbers assigned to them in later issues, editions, or 

All the letters originally printed in Dutch, under Leeuwen- 
hoek’s supervision, were translated into Latin and printed in 
that language; but the Dutch and Latin versions were not 
issued simultaneously.” (As a rule—but not invariably—the 
Dutch versions preceded the Latin.) Furthermore, the letters 
—whether in Dutch or in Latin—generally made their appear- 
ance a few at a time in the form of a brochure with a common 
title: while a little later another collection would appear— 
often printed for a different publisher and with a different 
title—and in this some of the earlier letters were often incor- 
porated. The final complete collections of Leeuwenhoek’s 
letters were made up of these earlier partial collections—of 
various issues—and new editions; and, in the case of the 
Latin translations, sometimes of entirely new versions corrected. 
and amended almost beyond recognition. 

The following is a short list of the chief printed versions 
—both Dutch and Latin—which I have myself been able to 
study, together with a few notes [in square brackets] which 
may be serviceable to others. The arrangement is chrono- 
logical (for either language), and the names of publishers 
are given in parenthesis after the place and date of publica- 
tion. Numbers are prefixed merely for convenience of present 
reference, and have no other significance. 

1 Cf. p. 356 swpra, and Dobell (1931). 

2 By far the best list is that given in Harting (1876, pp. 132-139): but 
this publication is itself so rare that few authors can nowadays refer to it. 
My own copy was most generously presented to me by the late Prof. M. W. 
Beijerinck—after I had for years vainly attempted to obtain one through 




Ondervindingen en Beschouwingen der onsigtbare geschapene waarheden, 
vervat in verscheydene Brieven, geschreven aan de Wijt-beroemde 
Koninklijke Societett in Engeland. 4°. Leyden, 1684 (van 
Gaesbeeck). [pp. viii + 8 + 32. Contains Letters 32 & 33, 
unnumbered and paged separately. Figs. engraved in text.] 

Ondervindingen en Beschouwingen der onsigbare geschapene waarheden, 
waar in gehandeld werd vande Evyerstok [enz. enz.]. 4°. Leyden, 
1684 (van Gaesbeeck). [pp. ii + 21 + 19. Contains Letters 37 
& 39, unnumbered and separately paged. Figs. engraved in text.] 

(a) Another edition of Letter 37 entitled: Antony van Leeuwenhoeks 
37ste Missive, Geschreven aan de Heer Cristopher Wren. 4°. [Lugd. 
Bat. 1696 ?] [No preliminary leaves: paged 1-20 (not 21, as in 
orig. ed.), and with different make-up.] 

Ondervindingen en Beschouwingen der onsigbare geschapene waarheden, 
waar in gehandelt wert vande Schobbens inde Mond [enz.]. 4°. 
Leyden, 1684 (van Gaesbeeck). [pp. iv + 24. Contains Letter 
40: unnumbered, with figs. engraved in text.] 

(a) Another edition, entitled: Antoni van Leeuwenhoeks 4Oste 
Missive, Geschreven aan de Heer Francois Aston. 4°. [Lugd. 
Bat. 1696 ?] [No preliminary leaves: pp. 1-24, identical with 
Ist ed.] 

Ondervindingen en Beschouwingen der onsigbare geschapene waarheden, 
waar in gehandeld werd over het maaksel van’t Humor Cristallinus 
[enz.]. 4°. Leyden, 1684 (van Gaesbeeck). [pp. ii + 26. 
Contains Letter 41: unnumbered, with figs. engraved in text.] 

Later edition: see No. 17. 

Oniledingen en Ontdekkingen van de onsigtbare Verborgentheden ; vervat 
in verscheyde Brieven, geschreven aan de Wyd-vermaarde Koninklijke 
Wetenschap-soekende Societeyt tot Londen in Engeland. 4°. 
Leyden, 1685 (Boutesteyn). [pp. 88, but mispaginated 79-94 
from p. 72 to end. Contains Letters 38, 42, 43; unnumbered, and 
with continuous pagination. All figs. engraved in text.] 

(a) Another edition [? 2nd] dated 1691. [non vidi.] 

(0) Another edition [? 3rd] dated 1698. Same title and publisher, 
but with letters numbered. 

Ontdekkingen en Ontledingen van Sout-figuren van verscheyden Souten : 
van Levendige Dierkens in de Mannelyke Saden de Baarmoeder 
ingestort ; ende van de Voort-telinge [enz.]. 4°. Leyden, 1685 
(Boutesteyn). [pp. 76. Contains Letters 44 & 45; unnumbered, 
and with continuous pagination. ] 

(a) Second edition, zbid. 1696: with letters numbered (but 45 mis- 
numbered 46.) 

Ontledingen en Ontdekkingen van het Begin der Planten in de Zaden 
van Boomen [enz.|. 4°. Leyden, 1685 (Boutesteyn). [pp. 78. 
Contains Letters 46 & 47: unnumbered, and with continuous 
pagination. | 

(a) Another [? 2nd] edition, ibid. 1697. Letters likewise unnumbered. 


8. Oniledingen en Ontdekkingen van levende Dierkens in